G4life, I have taught lots of classes, a few tips, you teach the class, don't let them get you distracted with Shaggy dog stories, and what if's, teach your course, and there is plenty of time afterward for the what if's, We practice a thing called FPPF, fairness, patience, persistence and fairness, 1st tell them what you are going to teach them, then teach them, and them tell them what you taught them. By telling them in the beginning what you intend to teach, you should now have taken control of the class, be prepared with visuals if possible, literature, overhead projector etc... You take the lead, be prepared and your butterflies will get better.
Best of luck.