JJ in 3rd hand of a sit'n'go

[ninja please]

i've been experimenting for the first time with no limit tournaments the last couple of nights. i'm a fairly solid limit player, but i am pretty inexperienced in tournament play, and have basically never played no limit. so, obviously, i am often faced with situations where i'm not sure what to do.

this is the third hand of a 5+1 paradise NLHE sit and go. starting stacks are 1000, blinds are 5/10.

i'm dealt JJ on the button. 4 players call the BB to me, and i raise to 50. blinds and first limper fold, 3 others call.

flop: AT3, 2 hearts (neither of my Js is a heart)
checked to third limper, who bets 20.

what's the play here? do i put in a raise, or just assume an A is out there and fold. i folded to the bet because it was so early in the game that i really didn't want to get caught up in a war with an A that probably will probably be showing down his hand no matter what my bets represent.

was this too weak?

and, as an aside, does anyone have any links or suggestions for links to reading on an intro to no limit play?