so, you probably were doing a little low-level sightseeing near the mountains/in the valley. hit some downdrafts over the top of the peaks or the side of the valley.
did you talk to your instructor about what happened?
btw, the carb heat did not depress itself because the teeth are worn as you said. the carb heat pulls itself off automatically in relation to how much power you are pulling. the higher you pull the collective the more it comes off.
of course i could be wrong, but i doubt any school would allow a student to fly an r22 with a faulty carb heat lever. but then again if they are letting you fly solo over mountains in a 20 knot wind who knows....