My car fell off the jack!

This actually happened about an hour ago. I took the wheel covers off and loosed the nuts from both tires. I lifted my car up with the jack and took the left tire off. Without thinking, I walked inside to wash the brake dust off the wheel covers when my friend came inside and told me that my car was lying on the ground! I walked outside to see what he was talking about and saw that my car had rolled off the jack and the rotor had slammed against the concrete! I jacked my car back up but it rolled off again! I finally wised up and used a stand, kicking myself for not doing it in the first place. My friend looked at the rotors and didn't see anything so I put the tire back on. I drove my car about 20 feet and now it is making some kind of grinding noise! How much damage did I do to my poor car? :Oops: