Hopefully you have enough of the fab. to take care of the mistake. But don't really consider it a mistake, just use those on the backing, and you won't lose anything from the error. Perhaps you might want to cover up the 1 with a small piece of painter's tape, (easy removable and no residue on your ruler) and this mat be a reminder of where you need to start your cutting. Just a thought. I think everyone has been in your shoes sometime or another. Really makes me feel DUMB when I do something like this. Good Luck.