What do I tell my parents??

I was all excited about going to my first homecoming dance, but now things are starting to change. In junior high I skipped all the dances and now that I was finally going to have a social life my parents were ecstatic. My mom let me buy an exspensive dress and offered to pay for tickets and everything. Homecoming is in a week and now I don't want to go. Some stuff has been going on at school with friends and boys and I just don't think emotionally I could handle being there. (sorry i'm so vague, but the situation is complicated) I can't tell my parents the real reason I don't want to go, we can still return the dress and everything and get the money back. They just don't understand how high school is these days. What excuse can I use to convince them to not make me go to the dance?