Foxwoods $1/2 NL my first hand AA, good fold?

[Nicefingcatch]

I buy in for $200 and I honestly don't remember how much villian had but I know he had me covered so let's say he had $300 in chips. Kind of funny guy UTG raises 20 preflop and every1 folds and he shows aces. Well don't you know very next hand it folds around to me and I pick up aces. I make it $15 to go and only the villian to my left who was the SB calls.
Flop:
K [img]/images/graemlins/heart.gif[/img] 6 [img]/images/graemlins/spade.gif[/img] 7 [img]/images/graemlins/diamond.gif[/img]

I lead out for $20 and he first says make it $30 but then says oh I gotta make it $40 to double your bet. I could have and prolly should have raised here but I just call. turn comes 9 [img]/images/graemlins/diamond.gif[/img] and I insta-check. He throws in two pretty green chips for a bet of $50. I really didn't know what to do here and thought for a while and flat-called. River comes 10 [img]/images/graemlins/spade.gif[/img] and I check again. He bets $75 and I only had $100 left so I really thought he could easily beat my pair of aces here. Again, it was my first hand I played at the table, I didn't know how he played and I didn't want to lose a buy in right away. So I show my aces and say you must have flopped a set and finally folded. Was this the right fold? Would you have called the river bet? Any help on to play this hand better please?