Even though we've just carried a baby for 10 months (where they get 9 months, I don't know, lol, it closer to 10!) and had them and are now caring for a newborn, it doesn't make that post pregnancy body any easier to deal with. (It really should though!)
I had to go to my husband's graduation 4 days after having my second baby. It was the first time meeting all his classmates. No matter what I put on, I looked aweful and all I wanted to do if cry.
Lucky for me, everyone knew I just had a baby, but since 95% of his classmates were these 20-something skinnies that had nevr had kids, they didn't understand just what that meant physically. However his professors who most of them had children, were more than sympathetic.
Tell EVERYONE you just had a baby. At the very least it will help you feel like people are not judging you. Try not to think about it. Ok so I know that sounds impossible, but if you make an effort to talk to a lot of people, you will find that when you are in the middle of a conversation you might forget that you feel uncomfortable in your clothes.
And DON'T compair yourself to the other girls!!! First, there are probably some that never had kids, and we know that their bodies are not going to look the same. Or if they have kids, unless they just had one at the same time as you, do not compair!! (Even if they did, still don't compair, lol, it only leads to stress!!) I don't know if this is your first baby, but even a few months after having a baby, can make a big difference.
Try to relax and enjoy the ball. I know postpartum, our bodies feel like blah, but its only temporary. We just just brought life into this world, and that's no easy task! Besides, the day will come when you will look back at photos and say "oh remember that? I just had [insert your baby's name here] I had a good time that night!"