What should I wear to a really good friends bat mitzvah?

OK, I'm really petite for my age *im age 12 but im only 4ft 9in.* but I have reallllllllllllllllllllllllllllllllllyyy… Long legs =)! but i have a small bust xD and I don't know what to wear! O and my crush is going to be there =D and I would preffer something black or blue or white*black & white* =) or green w/blue XD