[Fantam]

I dont think that you needed to cap this flop HU.

You already raised villain's initial flop bet, which could have meant that he had top pair, a flush or straight draw. His 3-bet suggests that he may have 2 pair or better.

In any event, capping the flop is unlikely to make him fold and wont really provide you with any additional information regarding the strength of his hand.

Also you need to bear in mind, that if you are behind that apart from a runner runner straight that you only have 2 outs to improve to a set.

I dont think that capping the flop is a terrible mistake because it only costs you one small bet. However, I think that I would have just called villain's 3-bet and waited to see the turn.