You just gotta dance. There is a movie from the 70s during the disco craze starring Donna Summer called Thank God It's Friday. It has one of my favorite lines - "Dancing, everything else is bullshit". Watch it and you'll have no choice - your body will start dancing.
Do yourself a favor and just do it. You'll have a blast. Here are a couple of hints:
1. There are tons of wonderful people who won't care about your bag. There are also some who might be put off. Don't worry about them - just be yourself and you'll find the right friends.
2. Don't let it define you. You don't need to have it be the first thing someone knows about you, it can certainly be more of a "by the way" thing after you know someone better. People on the dance floor aren't going to notice or care. People are mostly worried about whether they look stupid dancing.
3. There are many wraps that can keep it discreet - try ostomysecrets.com. With a wrap you can be hugged, squeezed, dipped and promenade the hall. There is no move where someone will ever know.
4. It's usually air that causes it to balloon quickly, and if you have a new bag with an unclogged filter, the air will dispense on its own. Put a new one on when you go.
5. I find that physical activity slows down or even stops the output, so if you are dancing, it might not be an issue.
6. If you do have output, proactively empty. This is actually easy for a female, since you are already in a stall. If you are worried about odor, drop some mints (Tic Tac or Altoids or Mentos) in the pouch.
7. Since most people have no idea what it is, I think Rob's comments are right on - people can be curious. The biggest thing is your own attitude. It is certainly nothing to be shameful about. In fact, everyone has something that makes them different - some people are bald, some wear braces. I think the thing that throws us is the poop aspect, which can seem kind of nasty. So if you just think of it as a medical appliance, and no one else ever really needs to be exposed to the unsavory aspect of poop, it's really not such a big deal.
So please, please, please go dancing as soon as you can and report back to us. I think you will absolutely love it.