I was pulling out from parking lot, but went too far on to a road, so I backed up. Suddenly I felt that I hit something. It was a car, but I didn't notice it. When I got out from my car, I had 2 small scratches on a rear bumper, and another car had a rear tag (sorority sign) bumped inward, but no scratches. I mad a picture on a cell phone of the car immediately. Than we decided to exchange our information, and before doing so the other person asked me to sign a paper where I would say that I backed up and hit the car, that it is my fault and that I acknowledge it. I refused to do so, and asked to call a campus police. When police came, an officer gave us information cards to fill out; we exchanged those cards, and the officer left. No police report was made. I don't know if I must inform my insurance company about this minor accident? What should I do if that person will try to claim that I damaged her car? How can I prove that her car really did not have any scratches (except it is an old car, so it had some scratches already)? Thank you!