If I hit someone's car I think I will just drive away.
That sounds like a bad idea. Why would you drive away?
I don't want to get in trouble and then I'd have to pay a lot of money.
If you hit someone's car, you need to hang around and provide them with your insurance. If you drive off without providing your insurance information, then you can get charged with fleeing the scene of an accident.
Okay then can you call the cops for me?
You should go back or call the police yourself and admit what you did. You would want someone to do the same.