It would have been tought to call in that situation, but there are 2 schools of thought here. One would be call and go to the limit, even on the first hand because (even though it is hindsight) if you are head-to-head, chances are he does not hve both A's and probably not a higher kicker. The problem is that you have no way to know that he has pocket T's. That would have made you a big pit, but been very risky. If you would not mind risking that much of your bankroll, then go for it. The second option is similar to what the others are saying. Either watch for a few hands or play tight for a few hands. I usually do this as I hate to lose money, especially right off the bat. I usually even fold a hand that I may think would be good on other occasions, just to keep from losing my stack.
To be honest, I would say you did the right thing for the situation. The A-T is a tough one, even though it could be a good hand. If a T comes out your are toast against pocket T's.
As with all these others advise, I usually go with patience and slightly more conservative play until I have a handle on the other players.