I think hit a pedestrian! What should i do!?

I was on my way home from work today and i stopped at burger king to get some food. As i was pulling out i leaned over to push in my car's cigarette lighter and when i looked up all i could see was the terrified face of this older lady and then -Smack!- she rolled right over my windshield. I wanted to stop, to make sure she was alright..... but i've never done anything bad before, never been in any kind of trouble with the law. I panicked! I hauled *** out of there as fast as i could, drove home, and sat down on my couch. I tried to tell myself she was alright, that i couldn't have hit her very hard. But now i can't sleep, i just keep seeing it happen over and over again? what if i hurt her, what if she cracked her skull on the pavement or something and she died? what if there is a police report out and they're looking for my car........ A part of me wants to call the police, tell them what happened. But if i get in any serious trouble i could lose my job! I don't know what to do, i'm freaking out..... someone -PLEASE- help me!