Don't be ashamed of how you look. Getting contacts could help if you think you're ugly and eventually the braces come off. Besides, having a big chest really isn't that great. I'm a C but I have horrible back and rib problems. Also, guys don't look at that (if that's what you think) and if you're into guys that do, you're looking in the wrong area for a boyfriend. Also, you're just 12. Focus on life and your studies and not how you look. You're still young and have a lot of time to try and look 'pretty'. Here's a secret though: Inner beauty is the best in the world.
Just let time go by and grow naturally, it'll pay off. I promise =)