How do I really improve my confidence/self esteem(not too long I hope lol)?

You're young :) trying new things or things you've always wanted to do can build confidence/self esteem.

Working out and eating right does wonders as well...

I think you should try to do some meditation and focus on building confidence. Surely you have access to leaning different ways of meditating. If you dont, ask friends.

Girls who are worth being with like guys who are just themselves. Being shy or antisocial is a way you deal with life that is not beneficial to your life or health. If you want to change, believe in yourself and do it!!!

Although this is, in a way, totally unrelated to school and breaking out of your shell...what I'm about to suggest will indirectly give you confidence which will help with your problem.

my suggestion is to rock climb.

you don't have to go outside and rock climb, there is most likely a rock gym in your area. it doesn't matter if you have never climbed before because when going there they will show you how to belay and tie your knot...etc

I started climbing about 3, almost 4 months ago. I must say that I am DEATHLY afraid of heights. that being said, I always like to challenge myself. I look at what I'm afraid of and then purposely put myself in a situation where I am exposed to that fear until I get over it. I went climbing at first with one goal: to get over my fear. but something took hold and I can't seem to stay away from the rock gym. when you challenge yourself on a hard route and you achieve it it's exhilarating. and it keeps you coming back for more. I didn't realize before doing this, but climbing has given me a confidence that I never knew I had within myself. That is what you need to do, find something that frees you like climbing did for me. I suggest maybe giving it a try, it's more than a personal challenge, it tests you to your limits and with every achievement you grow stronger. somehow, in some way, it's a personal journey and grows your confidence, not just when climbing, but in every aspect of your life.

give it a try, I swear it will help you see the true strength you have within yourself and give you the confidence you need.