i put my car in park. it didt catch, my car started rolling

I'm very concern when I put my car in park and started to get out my car and it begins to roll. I know I put it in park and the gear did catch. This is a serious problem. What if I injury someone or kill someone over a defaulted part. This has happen at lease three times. Now I try to look my closely before I get out of my vehicle. I got a recall letter about the gear sh*t but nothing I mean nothing has been done to correct the problem.