50NL Should I slow down with my set here?

[hielo_uno]

Cry Me A River explained it pretty well. You have a good hand, you should built the pot on the flop, also you are charging a hand like J9s to pay to see their gut shot. In this case, he could caught his gut shot and stacked you.

Preflop is really bad too, just fold. ATs is not a great hand in early position.