Design want release from backing for print media

I purchased a roll of express print from Stahl's. Ran a design on my Roland 300i. Am using a medium clear mask, but can't the design to peel off on to the mask. Unfortunately have cut out 60 designs and weeded, it is partially coming up after much use with the squeegee, but letters are still trying to stay on backing. Help !!! Any suggestions as to what to do or suggestions as to what I may have done wrong ?? Thanks for your help. Tim