Traffic Accident Help?

I have a 1991 new yorker. A big old truck hit me. It was a Business truck so of course we have to call cops and the whole nine yards. Well he backed in to me at a gas station. It was totally his fault but the cop told me it was my fault because i failed to yield to a larger vehicle. I was behind him at the gas pumps and he moved forward, i thought he was going to turn so i moved up, then he backed up and hit me. We were at a perfect 90 degree angle so if he just truned his head back a little he would have saw me. So is it my fault? If it is how did i fail to yield when i wasn't moving?