When I put the vehicle in park and put the emergency brake on, the vehicle rolls about 2 feet before it stops.

My driveway is a down grade from the garage to the street, so when I parked in the driveway, I opened the door and the vehicle was moving backwards about 2 or 3 feet. I just got the vehicle at a used car dealer, totally love it but this scares me ! I didn't see a recall where this was mentioned.