call the company and ask the best way to remove it. i had one ruler that i could not get it off---called and they said it was not supposed to come off! i asked---well how the heck am i supposed to see through it then???and was informed it was not a *quilting* ruler- it was made for scrapbooking-i returned it-
you might try adhesive remover (available in pharmacies) or even a tbsp of olive oil may lift the glue-
good luck....
most adhesive removers are some sort of oil