Leeds fest help!!! i don't know what to do?

ok so a girl i worked with got tickets to leeds fest for her and her boyfriend and then they split up so she was saying she didn't have anyone to go with so i said i would. now...i WAS excited by this apart from the fact that this girl has recently been doing my head in...i mean really, the thought of spending the entire day with her is actually making me get myself really worked up and i don't know what to do. i have paid for my ticket but i'm frightened if i go i will just have a mive argument with her and ruin it anyway. i feel bad if i cancel because she could have sold both tickets but i really don't think i want to go anymore. what should i do help?!