If you were there last year, will you be able to see people who you got to know a bit last year? If you do and you haven't seen them since last year, then there's a whole summer's worth of stuff to get caught up with - you'll find out who is in your classes and hopefully there's someone in the class before lunch who you can chat with and spend lunch with.

If you get lost, just walk into the nearest classroom and ask the teacher where the room is that you're looking for. If it's between classes then there won't be anyone in there.

((I don't know if this will make you feel any better, likely not, but I'm a teacher and I totally get back-to-school anxiety. I worry that my class will hate me and that my coworkers won't want to talk to me. By the second day back that anxiety's almost always totally gone. I hope yours will pass soon too!))