Pooh, RA's right that you shouldn't worry about what you're wearing. The only times people notice what people are wearing to an event is when it's totally inappropriate, like an ex girlfriend coming to the BF's wedding dressed in widows weeds, or a teen in shorts, sandals and tshirt at a Bar Mitzvah, when all the other boys are wearing suits! Or, an example from my RL, how about the boy who came to the senior prom wearing a tshirt with a tux printed on it and a top hat and cane? After all these years I don't remember who it was, but I remember how bizarre he looked!
I'm sure you'll look lovely, because you will be shining out from whatever you're wearing! Just relax and enjoy yourself!