what do I do?

When I pulled into a parking spot I clipped a car/jeep parked to the right of me. The car to the left of me was over the yellow line and the car on the right (that I hit) was at an angle (which I unfortunatley did not realize until it was too late.) I hit the car's left rear bumber. My front right bumper was dented and popped off. There was very little damage to the car (a jeep) that I hit. There were no dents or impact marks. There was a small scratch
( it was Truely, a small scratch). I waited for the woman to return to her car. Since it was my car that had the damage, I said I didn't want to have to go through insurance. I gave the woman my name and number to cover her cost on compounding the scratch ( she wasn't even sure it would need it). We didn't call the police and we didn't exchange car info/insurance (just names and telephone numbers). The repair to my car cost $550 (new painted bumper plus labor). The woman recently called me (3 weeks later). She said she brought her car to 2 different repair shops and was given estimates at both for $650! I am a complete fool. I am being taken and I don't know what to do! I told her I didn't understand how a "scratch" could cost so much. She says there was a dent that needs to be "popped" as well. I apologized for the trouble and told her I would cover the cost (I am suppose to contact her this week). I am CERTAIN that the only damage to her car was this scratch!! What should I do? Is it too late to contact my insurance co.? Should I get copies of her estimates and pay when the work is done? She knows I wanted to avoid the insurance co. (I have several teenage drivers and don't want my insurance to increase). I also don't want my husband hearing about a possible $600 bill (althought it is my car and I work full time and will pay with my own money). I have this sick feeling that this woman is taking advantage and need to know how the best way to handle this mess. I deeply regret not contacting a police officer at the time, and turning into that spot!