Should I be worried about my girlfriend going to this party?

Look, just tell her you don't want her to go. Tell her you trust her and that you hope she has a good time though. Tell her to call you after the party when she gets home so you know shes okay. That way you know she's home and not with some douche bag. Then when she calls ask her how the night went and tell her you miss her and wish you could have gone to the party with her and say she probably looked hot in lingerie ;) Woman like compliments from the man she is with ;)