how to hide a gap in my teeth??

Don't hide it. If the people at your school can't accept 你 with a gap in your teeth, they're not worth your time.

I was gonna say wear a flipper over your 最佳, 返回页首 teeth but seeing the braces that won't work out. I donno sorry to say.

I am assuming that 你 are saying this because school is starting and 你 are afraid people will dislike 你 because of a gap in your teeth.
A gap like that isn't really that big of a deal, my teeth are all arranged strangely and their place is so messed up, they say braces won't even help, and on 最佳, 返回页首 of that my teeth always look dirty no matter how much I brush them, and that has never caused me any problems.

But to answer your question, just keep your mouth closed whenever 你 can, and don't look people straight on when 你 talk to them.

My friend has an expander too. Well I don't really think 你 can hide it, but maybe just don't smile a lot.