Yesterday I hit someone's car and kept driving
Why did you keep driving?
I had a big fight with my mother, I was driving away from the scene of the crime.
You should never leave the scene of a crime. It's wrong to drive away. It's possible that there will be legal issues for doing so.
I'm going to hire a lawyer.
Yeah, that would be the wiser step to do now after what you did. How about working with your lawyer, to try to make up for your mistake, be responsible, and compensate the victim properly? It would be safer to do it this way with all the protection.