This sounds like you might be a little too conservative in the later stages, though like Beriac said we really aren't getting enough info about your style to analyze it.
The key to HU play is aggression. You really have to be almost every pot at this point; probably 90% of them plus or minus. Your hand selection goes down the drain, and much of your play is raising from the button with just about anything because you have position on him. I raise from the button probably 80% of the time, and if my opponent is passive (heads up, you might aswell call that weak), then I'm raising every pot PF. Raise PF, continuation bet the flop. Raise PF, C-bet the flop. Raise PF, C-bet the flop. It just goes on and on until my opponent pushes back, and hopefully I catch him with an ace or two big cards, or maybe a pocket pair preflop, and set him in. It's also often good enough to call down/raise with hands as weak as bottom pair - but trust your reads.
Anyways I rambled a bit there, but remember that the key thing is aggression. You need to be in almost every pot.