While I'm certainly glad that you're alright, that you didn't have to shoot anybody (the absolute last resort, without a doubt), and that you made decisions and acted decisively, there is still something that bugs me a little. As a couple of other posters have mentioned, what if the perp had not been bluffing? In my view, putting myself in your place, a threat is a threat regardless of the underlying truth because at that moment I don't (and can't) know whether the perp is armed and really intends to kill me. I have to react as if my life were in danger because for all I know it may be about to end within seconds!
Now, don't get me wrong--my first (and only, at least initially) priority is surviving the encounter, preferably unharmed, and without shooting anybody if at all possible. If I could escape quietly without endangering myself or even drawing my gun, then that's what I'd do. That said, what I would NOT do is allow a bad guy to outdraw and shoot me first (especially in the back) if I can prevent it. There's nothing wrong with retreat being the preferred option, but any notion of "duty to retreat" ends as soon as my life is actually threatened. I'd say that a guy who is trying to rob me reaching for his pocket in a threatening manner must be treated as a serious threat, and my response would be pointing a gun at him, ready to shoot (and evade any incoming fire) in an instant if he continues to escalate the situation.
If this is not a valid use of a gun, then aside from the obvious case of a home invasion, when can one use a gun (shooting only if forced to) in self-defense and for what reasons? I'd rather not wait to get shot first if I could have threatened the bad guy and thereby possibly avoided bloodshed altogether (or at least my own).