Is it that serious ??

What is the name of your state (only U.S. law)? North Carolina

I was in a parking lot, opened my door and accidentally hit (with my car door)the car parked beside me. The person that owns the car was sitting in their car at the time. Instead of immediately calling the police, the girl drove off. Do I still have to pay for the damages done to her car even thought it wasnt reported until later? Since she has an older car the scratch couldve already been there before, and I dont have any marks on my car.

My car is white, the car I hit is blue.....

Yes, you are still responsible for the damage you caused if she chooses to pursue a claim. Your insurance should cover you.

did you exchange information with the person?