I'd bet the turn i think. UTG probably has some random pp which probably missed and who knows what the button has. I'd have fired the flop tho as this is a board which will miss both of them enough to make the cbet profitable i think.
Why are you 3 betting so small? I'd make it at least $8 here from oop. You are giving btn such good odds
to call here that it is pretty hard to define his range. I'd just presume UTG is bad and just completely overcalled to setmine. I really can't see a 8/5 limp calling with much else. Your 3B size is just bizzare tho and makes this hand really hard to play.