I agree with Scubba, upon reflection I'm sure you feel the same way, you already realize the turn bet was insufficient, probably realized it by the time you had to place your river bet which is why you went to $45, here is where checking would be excellent and almost might help you turn a previously poorly played hand into a winner, if the opponent is seduced to bluff.

I like that you did not get crazy and call the all in, my gut tells me he had pocket 5's, so I don't think you wanted to lose the rest of your stack to see those.

takes Scubba's advice next time and check on the river, than call a reasonable bet if you are forced to. Never bet the river when you don't feel it will make you money. Inferior hands will fold, while dominant hands will call or reraise.