Quote from clut on June 9, 2012, 5:06 am

I also play on a mac, and I have the same problem... If I accidentally zoom in too far (which is very easy to do on a magic mouse), then I can never get that level back again... however, whilst there doesn't seem to be a solution, there IS a prevention method...

SAVE SAVE SAVE.
I always hit ctrl+s to save my chamber before I build it, so if/when I ever zoom in to far and lose the level, just exit out of the puzzle maker without saving, and then go back into puzzlemaker with your map, and it'll be exactly where you last saved, zoom level and all!

Save frequently, and you'l be fine.