Rolleiflex film count back to 0

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.

When you opened the back the counter reset, and since the feeler mechanism in the camera felt the thickness of the film, the counter was engaged and turned to frame 1. You probably lost at least two of the last frames of the film.

Advance the film to 2, press the shutter release, then wind to 3, press the shutter release, wind, and so on until you have wound up the roll, and then remove it from the camera as normal. The counter will reset normally for the next roll of film.

Good, thanks. I thought it didn’t shoot at all, even though it everything looked normal.