Hey! If you have over 100 pounds to lose, and you've lost 30, then that is great, but you are probably still pretty large. It could be that you're nervous because your body is afraid you're going to hurt yourself.
If you are serious about doing this bootcamp, get a copy of the program you'll be following, and take it to your doctor.
Get his or her opinion about whether you are at a point where you can realistically do this level of exertion without hurting yourself.
The place running this will probably have people sign a disclaimer anyway.
It really is possible to overdo exercise and do damage to the body. Just last week I had 'workout' session with a trainer, and I thought she'd kill me. My heart rate was through the roof and I thought I was going to pass out. She was all of 20 years old or something, and she had the nerve to say that I ought to "listen to my body" more--in other words, she was putting it on me. Well, my body says, don't use that trainer again!
Seriously--if you're afraid of doing something there may be a good reason.