If it's been out of the shop for a month, you dont' want to try to re-activate the adhesive (IMO). Re-print, and hope that your colors aren't too far off, and learn your lesson.
Unlike Adam, I use primer (in certain situations). And, depending on the vehicle type, there are other tricks you can use. For example, on Sprinters, there is a notorious recessed area that blows many people's minds. Easiest thing in the world to do with it is cut about 3 pieces of .030 magnetic to size, stack them, and lay them into the recess. Now, wrap over it. Done.