If the car isn't obstructed, and it probably won't be if the carjacker wants a quick getaway, what's wrong with just flooring the accelerator and scooting away?
We can what if everything in a very short video...
What if there is traffic blocking you in?
What if he shoots as you drove by; at 60 MPH you are going 88 feet per second, a 9mm is going 1200 feet per second, your kid may lose...
What if, what if....
You can only hone your skills overall, and then deal with the situation through the strength of superior skills!!!
Then the bad guy, before he dies, can what if, himself to death!!!