3 to 8 from out of position is rather small, especially at 5nl. I'd make it about 11-12.

On the flop I'd like the sizing vs a reg or in a higher stakes game but again i'd size larger here, like 13-14.

Turn, you can comfortably bet fold here, people just never raise your bet without at least two pair and plenty of worse hands will call. I like the size.

River, yeah you should bet or check fold as a general rule here. i'd bet fold again, like 21 or something. You can do highly exploitable stuff like this at 5nl to get thinner value or get away with a few of your chips when beat. You could even bet like 15. There are a decent amount of worse hands that could still conceivably call a bet, and two pair/set was likely to raise at some point.