I think you psyched yourself out here a little bit, which happens to most of us at times. Against this opponent, perhaps value-betting $100 on the river was an option? But given the fact that you don't think this opponent would call with one pair (though, given the speed of his calls on the flop and turn, are you sure?), your decision is not that bad. One thing to consider is that one pair will often call a half-pot bet in spots like this, hoping you're on a busted flush draw.
Here's a hand w/ a somewhat similar river decision (a much weaker hand, but similar principles apply):
Another river decision