I actually had the same feeling, but that's because I'm pretty competitive and hate losing or being shitty at anything really. So I actually weight lifted for an entire year to build an extra 10lbs of lean muscle cuz everybody had an average weight of 185 north to 200+. But that's just me I wanted to compete right off the bat with intermediates and be able to hold my own. For you though...just relax and enjoy it. You'll be sore, tired, muscles aching, gas in the middle of pad workouts, but that's everybody. I'll tell you one thing though. You'll gain a whole new appreciation for what the fighters go through.
Again, just go in there and have fun!