Did they give any in-car instruction, or cut everybody loose?
Glad you had a good time. Hook set!
Two things, though: ALWAYS look where you want to go, not at where you're afraid you might go. This is a hard thing to break, but very necessary, because the car will almost always go where you look. When the back end started to come around, you instinctively looked to where the car was going to slide, and that's where it went. But if you had kept looking all the way through the corner, chances are really good you would have saved it.
Second: Keep your hands at 9 and 3 instead of 12 and 12. I never have figured out why newer track/autocross people do this (my wife used to do it too), but you have way more control with your hands at 9 and 3. From a dexterity standpoint, you're better off driving one-handed than you are with both hands up top.