I'm trying to understand your situation. You were in the passenger seat and the guy jumped into the passenger seat? He fell out when you sped away? Do you mean he leaned in through the window.
I have to agree with others that say they would have had the windows up and the doors locked in this scenario.
As far as drawing my weapon I will only do that when the situation has escalated to the point where I expect harm. Once someone is on top you, and you've drawn your weapon, but not used it, you have increased the chance that they could disarm you and use it on you.
I'm not saying I would have shot someone who was leaning in the window and asking for my money...especially someone who wasn't brandishing any kind of weapon. Speeding off, which was obviously possible was the best choice.