Home game question.

[phixxx]

Had a recent hand in which I was playing a friendly home game. My buddy made what I thought at the time was a HORRIBLE call. We were playing 3 handed, and I started with Qc3c and he called my opening raise on the button from the BB with Ac Ks. The flop came down 2c 4s 5c. I check-raised him all in (stack sizes here are irrelavant) and he instacalled with his AKo (very agressive player). It turns out that his AK holds up after two blanks hit. When I first looked at the hand, I saw myself as a huge favorite, with a straight/flush draw and his ace being dead due to it completing my straight. However, when I looked it up on an odds simulator, I am only a slight favorite. How can this be? If someone can go over the numbers or explain how I am only a slight favorite with this holding it would be appreciated.