It sounds to me like you have black and white thinking. I used to have it too. In my mind people were either beautiful or ugly, smart or stupid, popular or unpopular. I couldn't see how somebody could be in the middle and just be average or at least I could not see myself as in the middle. I wanted to be "model beautiful" but because I was not I thought I was ugly. Now when I look at pictures of myself when I was younger I realize that I wasn't ugly in fact I was sort of cute. Not gorgeous but cute. I wish I had realized that back then because I had low self esteem too.

It is fine to want to better yourself but please accept yourself for who you are now. If you don't like your glasses get a friend to help you pick out some attractive ones. If you don't like your hairstyle try something a little different. Be realistic about improving yourself for what you value not what the cliques in high school value. And remember that one of the most attractive things a person can have is self confidence. Try to build yours.