I started out working fast food jobs when I was younger and I can completely relate to those feelings. Starting any new job is overwhelming. You can't walk in and be perfect on day 1 though! Give yourself time to learn and don't be afraid to ask for help. At every job I've taken, I have always found at least one person who is very kind and willing to help. I bet there is someone there who will help you if you're struggling.

I really hope you don't decide to cancel. You will feel very proud of yourself if you do this and stick with it.