Personally, I feel that you should have the absolute right to shoot the guy. I believe that the law should hold you immune from prosecution for putting a slug right between his eyes. You would have done the world a favor by eliminating this guy. And, if I somehow got selected to sit on your jury, no amount of convincing, arm-twisting or legal trickery could get me to convict you of anything.
BUT, you did the right thing....under the laws that we have today. You would have been justified in putting the car in reverse and driving off with him hanging from the window. You would not have been justified in shooting the man, especially if he was unarmed. You actually did a nice job diffusing a dangerous situation at minimal cost to you.
Oh, and, there ain't no way I'm going to get selected to sit on your jury.
Personal story: Years ago, I had broken down in a parking lot near a rough side of town - was in the middle of replacing a radiator hose on an older car. It was about 11:00 pm and I had my girlfriend with me. I noticed a man slowly walking across the parking lot toward me - no one else was around. I acted like I didn't see the guy coming. Waited until he was within 10 feet from me - the guy never said anything. I turned around and faced the guy with a large screwdriver - looked him straight in the eyes and told him I was going to F-ing kill him.
Was I right? Legally, no. Am I still alive? Sometimes you need to be the first to act, right or wrong, doesn't really matter does it?