For other people -- especially newbies -- who may end up reading this thread, I have also seen multiple cases where the display of a handgun in a road rage situation resulted in being charged and convicted. The key differentiators in your case are threefold:
- You were boxed in and had no other way to escape. This is key.
- Hitting your window makes it unlawfully attempting with force to enter your vehicle, thereby helping to justify deadly force.
- Dialing 911. The legal system is set up to assume two roles in the drama: victim complainant and perpetrator. Better to establish one's status as the victim complainant.