I think you extracted as much about as you could. More than I would have but that is not necessarily a good thing. You just played it weak enough to bring along this opponent with his pair of 5s. As played I raise that river. With this weak betting you can’t seriously be afraid of a boat.

I bet that flop. He may call with his pair hoping for an A. More importantly, if he holds a K we can extract much more $ from him.

I guess there are two ways you can look at this. You have a hand and a flop that allows you to slow play.
I look at it another way. You have a hand that is very, very likely to win at showdown. Because of that, I am going to try and get a lot of chips in along the way.