A BE58 cabin door popped open right after takeoff. The distracted pilot returned to land on the wrong runway because while dealing with open door he had to reassure the non pilot passenger in the right seat that the aircraft was flyable.

Narrative

Departing with one passenger in the co-pilot's seat; the cabin door popped open and startled the passenger and myself. I asked the Tower for permission to make left traffic to land. I believe I told the Controller at that time it was not an emergency. The Controller cleared me to land on Runway XXL. On downwind; the door opened further and the cabin noise increased dramatically. I was trying to reassure the passenger and fly the pattern while complying with the Controller's clearance. I inadvertently landed on Runway XXR. I only realized my mistake when the Tower Controller asked me to contact the ATC Supervisor via telephone. I believe I landed on the wrong runway partially because of the noise and the confusion as well as spending too much time reassuring my passenger that the door would not open all the way. Also; Runway XXR is much longer and wider than Runway XXL; so I didn't even see Runway XXL; I only focused on the bigger runway. In the future; I would make a point of paying better attention to the clearance and also ask for landing clearance verification on short final.