Incident occurred as I was waiting third in line to add fuel to my Audi. Usually when I am in a long wait I put my vehicle in neutral and to move forward then I have to put my foot on brake to change gears. In this incident I did just that when car in front moved up, but the car suddenly accelerated forward quickly and hit with force the car in front. I put car in reverse to back off with intent to shut down car to exit in order to assess damage and provide insurance information. Instead when I went into reverse the car shot uncontrollably backward 20-30 feet at high speed striking another car entering the fueling area. In either the forward motion and or the backward motion of car did the sensors or brake assistance system deploy. The car will be inspected by both Audi America and also by a third party appointed by my insurance provider.