Hello! Being a cosplayer that has had braces, I know how you feel. Braces are something you can't help, but they will not make your cosplay look bad! If you feel self-conscious about it though, you simply don't have to smile with your teeth. As much as braces are a bummer, in the end you'll have very pretty teeth and many years of braces-less cosplay ahead.
Works in Progress:
Shinji: Neon Genesis Evangelion - Link: Windwaker Link - Intern: Welcome to Night Vale - Celes Revamp: Grand Guignol Orchestra - Near: Death Note - Ed: Cowboy Bebop