Good Luck!
Keep in mind that you are not really competing against 250 gymnasts. First of all, you are going to be separated into age groups. More importantly, you are competing for yourself -- to do the best you can. If you do your best, or close to it, you will always be happy with yourself.
My dd scored an all-around in the 20s in her first meet, which you will find is not that great, but she had a great time and stuck with the sport. Next month, she will be representing the United States at the World Maccabiah Games.