Personally i would go. Have some fun and when you enivitable conversaion with the girl happens be polite smile alot then just move on to talking with someone else when the plesentaries are done. no one is asking you to maintain anything more than a 2min convo with her. its unlikely your even on her rader so dont stress it, you've got nothing to prove to her, no points to win no score to settle. be cool and do your thing! i doubt your still hung on her per say and just worried about the social aspect of it all, in other words this whole thing just stems from you wanting to not come off not needy or insecure so that you can 'impress' her. scratch this whole concept from your mind, to reitterate you have nothing to prove to this girl. she's just a girl in your reality and not by your post a very nice one at that. This means you have even less reason to prove anything to her.
if you think it would help, go with a mate so you have someone you can have a laugh with. in other words go met some new people and enjoy yourself!