How to stay calm during huge test??

So I have my first AP exam tomorrow, and I'm really nervous because I have bad anxiety and normally I have special location so I take the test by myself, but I don't have it for this test and I'm really worried that I'll panic. You're not allowed to leave or bring food/drink in, so I'm really freaked out. You're also not supposed to leave the classroom. I always feel so pressured and claustrophobic, I worry about what other people in the room may think of me if I freak out/panic. Help? :(