Redoing levels

I have been playing Supercow for some time now and this is the first time I have had a problem with the game. I had just finished level 7 and was moving on to level 8 but had to log out as another member of my family wanted the computer. When I logged back in I was sent back to level 6. This happened a couple times. Now it is just making me angry that I have to redo levels over and over and over again.