First, if one of my college professors had ever made me feel so uncomfortable by their behavior that I had to leave the class I would have reported it to the Dean of the College. I'm paying for that education and I want my money's worth.
Second, I agree with those here who have questioned the definition of "Terrorist". One man's terrorist is another's freedom fighter.
Third, I guess it would depend on how the gun rights were removed. If the second amendment was actually repealed through the proper mechanisms already available, then you (as a citizen) would either be compelled to turn them in, leave this society, or fight to overturn the government. Maybe at this point you are a terrorist. However, as long as the Second is a civil right and stated as such in the BoR, it needs to be respected as such. And it recently was by no less than the US Supreme Court. Until repeal, you are a civil rights activist.
Your professor has a right to his beliefs. He doesn't have a right to browbeat you in class over your disagreement with those beliefs.
ETA: Was he just baiting you attempting to get a better argument out of you? Could be. Go ask him before you go to the Dean.
MSSA Life Member