What you are supposed to do depends on your state laws. For instance in California if you hit or sideswipe a parked car the law requires you to try to find the owner. If you are unable to find the owner, or driver, of the vehicle you have to leave behind (in a conspicuous place) a note with your name, address and an explanation of the accident. If you are not the car's owner you are also supposed to leave the name and address of the person that owns the car you were driving.
After leaving this information California also requires that you notify the local police of CHP by phone or in person as soon as possible. Many states have similar laws. You did the right thing by leaving a note with your contact information behind. If your state has laws requiring you to notify the police, you shoudl do that too. The next step is typically waiting for the damaged car's owner to contact you.
When they contact you, you tell them what occured. It will be obvious that there is a responsible party, but many factors go into a standard side-swipe accident. Do not lie. The article titled What To Do Immediately After Being In An Accident will help give you a complete overview for an active accident. The most important aspect of that article is this:Once you are away from the scene it is time to contact your insurance company..... Remain in contact with the insurance company until your settlement is negotiated completely.