Recreational Vehicle Lpg Tank Valve/gauge problems of the 2002 Chevrolet Impala

I was driving the vehicle and when I came to a stop to pump gas I left the keys in the ignition I placed the car in park. I turned around to place the pump into the gas gauge and my car was rolling down the hill and I had to chase the car open the door and stop the car. When I got the car to a halt position. I tried to take the key out the ignition and couldn't get the key out the ignition. Once I was able to get the key, the key slot was turned at 3:00 position and not a 12:00 position when a key is removed from a ignition. After the key was removed the car started to roll again and I had to place the "emergency brake" on to keep the car from rolling. Once I tried to turn the car back on after pumping the car started up and I placed it in drive pressed the gas pedal and car stalled, I placed the car in reverse and pressed the gas pedal and the car stalled. My car has not worked since.