What white haus said. Offer, after all your useless labor....... quote it by starting over with new material. Explain to your friend, you cannot get it off. Most likely the conditions have bonded the two substrates beyond your control or either the wrong vinyl was used and have also bonded beyond your capabilities. Years ago, when we hand lettered awnings, they could not be used over for obvious reasons. I don't see why you can't do the same.