If, by your own admission, you are crap, the sound guy may be keeping you low in the mix, so as not to have it sound too bad out front. He will likely not want to tell you this for fear of hurting your feelings. I've been in a similar position when mixing. It's a difficult situation. Yes, the idea of a jam is that everyone (within reason) gets a chance to pitch in, but you still want to keep things sounding as decent as possible.