I hope you did more then just some group riding, you could very well be bumping shoulders,elbows with other racers, if this happens stay relaxed. Keep your head on a swivel, be alert in the turns, no doubt people will be diving the corners. A lot of people get dropped in their first race, so if it happens to you don't sweat it. Racing will be like nothing you can imagine, you won't know until you try it. Like Crimson said, enjoy the pain!
If the guy you are following starts to let a gap open between him and the pack go around him ASAP, if you start to get dropped you will have about 10 seconds to catch back on, after that you will have no chance. Most Importantly have fun, bike racing is addictive.