I'm too shy and feel insecure at the gym without my sweatshirt

Hi! My friends invited me to a zumba and fitness class in a gym.
I've always been so shy and I did not really like dancing, but some friends of mine convinced me to break the ice because they say I'm too thin and I need to do sports.
I work at office and never take time for gym, sports or anything, so I admit they are right.

Today I went to gym with a few friends of mine wherea free trial lesson was held. They accompanied me to the locker room where free tanktops offered by the gym were distributed to encourage new members to subscribe. I took a tanktop of my size but decided to stay covered with my turtleneck sweatshirt and I zipped it up all the way so that even a part of my mouth was covered. It's a grey sweatshirt with fleece inside which I bought when I visited NY many years ago and it's one of my favorite peace of clothing. It makes me feel confident and cozy. You can see it in the image below..

Then in the classroom almost everybody was in their tanktops and dresses like that. A few girls had some shrungs but they threw them at the bottom of the room very soon.

After the first exercises a friend of mine came to me and asked me "do you have a top under your sweatshirt don't you?"..i only got time to answer "yes but.." and she grabbed my zipper, opened it down all the way and pulled my sweatshirt out of my arms.
The warmth stored inside my sweashirt suddenly disappeared and I felt so umconfortable with that tank top which left my arms, my neck and my dull skin totally uncovered. She was about throwing my sweatshirt away but I insisted to keep it tied around my waist at least. Of course it was no longer protecting me but keeping it with me just gave me a chance to put it back on all zipped up at the next pause.

It did not work because during some exercises my sweatshirt swinged and waved around my waist and hampered some fitness dances. The instrcutor, a strong muscled woman, was walking around us to correct our posture and when she got to me she took my sweatshirt off my waist and said. This sweatshirt is hindering your training, let's take it off the way! My friends were laughing and she read aloud a label inside my sweatshirt and shouted "main fabric 90% heavy cotton, 10% polyester, inside lining 100% polar fleece 300". Then she laughed and said "wow! nice blanket for old ladies on the sofa!" and she used my sweatshirt to show some choreographies.

I was so sad when I saw my hoodie being shaked and flapped that way and even more worried when I looked at the zipper, completely opened, hitting the floor during the choreography. In the next pause I asked her to zip it up at least, so that the zipper did not got ruined and she said "are you really worried aboout this dorky sweatshirt?". Anyway she satisfied my request and zipped up my seatshirt before going on using it. She also said I should have bought something more attractive in NY than that heavy sweatshirt. According to her I need tshirts and doing sports to improve my body, not sweatshirts like that to hide my weakness.

I got my sweatshirt back at the end of the lesson one hour later. It was so creased and I think my sweatshirt never got treated that way anytime before.
Tomorrow I'll get to the next lesson and I'm afraid they would make me stay in that tank top again!

Whoa it sounds like your personal boundaries were disrespected by your friends/that teacher. I'm sorry they did not understand or respect your feelings.

Could you have a quiet word with these people explaining why you feel more comfortable in your sweatshirt?

Hello evangeline85: I'm sorry you had such a disturbing experience. From what you wrote, it sounds as though these people meant well (maybe...) But they certainly went about it in the most "ham-fisted" way imaginable! Kudos to you, though, for being willing to go back. Hopefully, over time, you will find these classes to be of benefit & you will begin to feel more comfortable being there.

I've been at the gym again the last days and took part to a few lessons of zumba, pilates and fitness.
Yesterday when I arrived to the gym I learnt that the class was to be held by a different teacher who is known for doing quite strong and strenuous dances. In the locker room my friends and other girls told me that my sweat tracksuit was unsuitable and advised me to wear just the tank top and the shorts provided by the gym. I simply ignored their advise and kept staying in my sweatshirt and sweatpants.

I told them I was cold but they did not trust me..it was not so cold inside the gym indeed, but I could not find the courage to explain that my tracksuit makes me feel protected and cozy and I need it to cover my thin body and dull skin!

Then we reached the classroom and there we had a first part of theorical lesson about nutrition, vitamin supplements, drinks, clothing and other good practices for zumba and fitness. When the teacher start talking about clothing she said that the gym provides our tank top and shorts meant for strenuous activity, like zumba, which is our program.
Then she asked me to approach and said everybody "this is a completely wrong clothing for gym, especially for zumba and fitness". She commented on my clothes and explained why those garments were not suitable. Firts of all she showed how my sweatshirt is made: long sleeves are not bad for warm-up, but heavy cotton and inside fleece are way too hot for anything. Only natural cotton is advised when doing sports. Then she said my hood was not suitable at all because we're inside a gym and not exposed to rain or wind at all, so it's just an additional burden on the wearer, especially because mine is so thick and cozy.
She stared to my zipper for a moment and said "this just looks like some hip-hop style dancers, but they usually wear their sweatshirt unzipped". She said that my sweatshirt is the perfect example of wrong piaces of clorthing for doing fitness because the zipper keeps the sweatshirt just skin-tight, it prevents perspiration and definitely keeps me too much warm and covered. More, a sweatshirt prevents a teacher from checking if our postures are correct because it's so bulky and thick.
"So let's start taking this oven off" she said. I had to unzip my sweatshirt and as soon as I opened it I felt it was no longer warm and cozy like before, the "NY" patched embroidery was no longer visible, sadly, because the sweatshirt's flap bended when I unzipped. Then she helped me take my sweatshirt out of my arms, she grabbed it, zipped it up and folded it.
I felt so embarassed in my tanktop: I still had my sweatpants covering my legs at least, but half of my tranksuit was gone and I really missed the warmth and shelter of my sweatshirt which was now down there on the floor and I was looking it with all its zipper, the fleece, the long sleeves and its hood which were keeping me covered until I got separated from them.

Then she started talking about my sweatpants, saying that even those are unsuitable to fitness and zumba classes. She asked me what fabric they were made of and when I said it was the same as the sweatshirt she advised me to take it off and staying in my shorts. Luckly my sneakers were right! I took my sweatpants off and my dull legs were now half-uncovered. She said "You all should have understood that fleece and sweat tracksuits are totally banned from that gym". Everybody was laughing and a friends joked by telling me "Say goodbye to your sweat trakcuit..memories of NY right? Just memories, now!".
The teacher learnt that the tracksuit was a souvenir of my visit to NY many years ago, though she said the gym is not the right place to wear it, that doing sports will allow me not hide in those heavy clothes anymore and that my sweartshirt and sweatpants are simply waaaay too heavy. She also joked about my clothes's fabrics, like the other teacher did too, and said that heavy cotton like that warms like an oven by itself, but with the inside lining of polar fleece 300 it just becomes unbearable. She advised against those garments for everyday, not only at the gym, since they are not breathable and keeps too warm for any indoor activity. The same is true for my sweatpants, according to her, who said she really can't understand why designers keep making clothes like these! She touched my sweatshirt and said "Look! You took it off 10 minutes ago and it's still warm inside..it's absolutely damn too heavy! And this turtleneck up to the mouth, this zipper is way too covering!".

Meanwhile I felt so exposed as my sweat trancksuit was there all zipped up covering nobody!

But I really don't understand whether my clothes are dorky or they simply do not want me to wear them again at the gym. I'm so unconfortable with this tanktop and shorts!

From what you write I think they are simply recommending clothing that will allow you to ventilate doing work outs, they don't want you to overheat. That is understandable.

If you really feel uncomfortable uncovered then perhaps you can reach a compromise? Maybe capri pants (or longer shorts) and T-shirt top might be a good half way between the two outfits?

I do understand feeling self conscious about your body but most people won't even notice the flaws you perceive about yourself.

I fear people clearly perceive my flaws because they do it every time I'm uncovered and tell me "You're too thin, do more sports" or "Your skin is so dull!".
Anyway I've already tried wearing a t-shirt but ended up with putting my sweatshirt back on. A tshirt is not covering enough for me, though better than a tank top.
If a gentle breeze comes through the open window at the gym it makes me feel cold unless I wear my sweat tracksuit that keeps me warm and insulated.

The same is for my sweatpants: capri pants or similar things are by far less covering and cozy.

After yesterday's class some friends of mine accompanied me at a tailor's shop where they asked the lady to give an estimate on making my sweat tracksuit lighter and more breathable. The seamstress looked at my sweatshirt and said it should not be too difficult. For a little money she offered to detach the inside polar fleece lining by unsewing it away from both the sleeves and the trunk. After that my sweatshirt would be waaaay lighter and should lose more than half of its warmth and insulation. Obviously polar fleece, when unsewed, would be thrown away.

Then she would cut the high neck transforming it in a V neck instead, though she would have to cut away the "NY" patched embroidery too, because with a V neck that part of the garment would not exist anymore.
As for the zipper, it would be cut away too and replaced by three front buttons, from the V neck to the bottom.

Similarly the sweatpants would be lightened and their polar fleece lining cut away along with the bottom part of them, so that I get capri pants.
My friends think I should accept this opportunity so that I could wear my souvenir of new york without being bulky and too warm for the gym.
I don't know whether I should transform my tracksuit or not, but I think they are right and I should convince myself.