"Warning Shots" mean you were not in immediate danger, hence no reason for deadly force.

I'm not going to give the chance to shoot back

"Warning shots" are a waste of possible needed ammunition, are not aimed in a safe direction as a rule and a tactical no-no.

Firing a warning shot indicates you are not in imminent danger.

A warning shot says that you were not in fear of your life therefore you could have used other means to stop the attack. If a gun is truly your only option then shoot to kill.