Your getting to its back was one action. I mean, I assume you were trying to get to its back to back attack it for extra damage?
Getting behind the creature in such a way without proper acrobatic ability was an action, since that was a difficult movement without proper movement based ability since all you are doing is using speed, not skill.
I mean, you are still going to win on your next Turn if both of your attacks hit. There is no doubt about that. Min/Max builds are pretty strong early game if done right (which you did, you opted for speed).
I assumed that was what you were going for anyway.
I can go back and edit this if you want me to.