"Limp preflop" is normally not recommended (Except for some situations), because many times we will complicate life in the postflop… At this point, all in directly on the flop is not bad, your hand is strong enough.
Once the flop came it was a generous flop for you, so I probably would have went on all in because you had the highest pair on the board and most likely no one has any higher pairs or they would have bet higher preflop. Only worry is if something is close to a straight, but there is a minimal chance that happens.
What do you want in free tournaments? There are a lot of inadequate people playing there. Go to higher limits or don’t play at all if you worry so much!