The boys basketball team cornered and flashed me in the locker room
What did they do exactly?
They forced me to expose my penis when I felt uncomfortable.
It can be difficult to deal with a situation like that. These people must be held accountable and you should speak with someone.
I feel very violated by what happened, and don't know who to talk to.
I know this is a difficult situation you're going through. Speaking with your school counselor would probably be the best first step.