For me open 2bb is ok when you have 18bb. I often prefer open jamming but it is freeroll and your opponents have similar count of chips so, probably noone call you. You want to eran sth so preflop raise is good.
On the flop bet is too small, 1bb to 5,25bb in the pot? too small, 1,75 or 2bb would be great. What is he calling you with? Queen? unlikely but no impossible, you have three of a kind. You are not afraid of anything here.
King on the turn is pretty safe, maybe some flush draws opened, maybe KJ, KT, AK, continue betting but not 1bb to 7,25bb! protect your hand smart! half a pot would be good.
Bet on the river is insane. 1bb / 1bb / and big bet immediately. Half a pot again. GL