Since the car is solely in your name, go get your car.
If you don't have a set of keys, take the title to a locksmith or to the dealer and they should be able to get you a set of keys.
However, in getting your car, be sure:
1) to NOT 'breach the peace' in taking it. You can't enter their garage to take it, can't force them to the side of the road, can't yank them out. Either take it from the driveway or a parking lot.
2) once you have the car and have driven away, stop somewhere and call the local police and let them know that you have "repo'd" the car. Give full information on yourself and the car. You do NOT want the other person reporting the car as stolen.
