Did I play this way too tight?

1/3 NL  I have about $600 in front of me, I had doubled my buy in and was waiting for my g/f to get to the casino so we eat dinner so I wasn't getting in the middle of that many pots.

I have 6d, 8d in the BB.  Action folds around and there are 2 callers.  Flop comes 5s, 7s, 9s.  I make it $15, there is one caller.  Turn comes Qh.  I make it $25, he calls.  River comes Ks.  I check, he bets $55 and I fold.  He then shows me a 9c. 

I know that I should have bet the river, but if he had a spade I'm out more money than just folding to his bluff. 

Yep, I'd have called or raised his $55.

Although, Godfather could be correct as well.  Depends on the player.