I'm going to church with my bf? D:?

I'm 14 and he's 16, and we're going for youth and then for lunch and to his house. Well I've never been to his church before and his parents are going to be there..so I'm so nervous. I'm scared to meet his friends LOL. SO help me out, on how to clam down and not do something stupid. Should I wear a dress or a skirt..?