I shot the entire roll of film on my 2.8F and after finished 12th shot I think I forgot to advance the film to the end. Now it got back to 0 and I opened the back door and there was a white paper. I advanced it to 1 and opened it in dark to check and the paper is still there. What happened and what should I do? Is it possible that I didn't shoot anything? Everything looked normal, each shot was counting normally as always.