Car Rolling in Park??

Ok I did something stupid, my fuel float screwed up but I figured I would pull the wires from the back of gauge to check for corrosion, ended up pulling some short of seilond. In order for me to get it back in I had to remove the colume clamp and plate in order to get my hand up far eough to put it back in. Well a thick shim fell out, I have no idea where it came from. thought everything was fine. But now I notice if I don't slam the gear shifter into park i will end up rolling. So anyone have an idea where the shim went or how to fix this problem???