1. Noticing the truck following you -- good. Situational awareness is crucial.
2. Getting out of your vehicle ---- good. Vehicle doors are poor bullet stoppers.
3. Placing shot COM -- good. Shot placement is crucial.
4. Saying that the shot literally knocked the BG off his feet ---- highly unlikely. If a handgun round knocked the BG off his feet, it would have knocked you off your feet, an equal distance, in the opposite direction.
5. Bottom Line --- You survived, so you did well.