I have been repairing iPads, iPhones and all kinds of devices in between. In the begening, the 3M tape would not do it. Either use double sided RED TAPE which works wonders and you wont have your customers coming back saying that their iPad screen is lifting off and also whenever you repair the iPad 2,3,4 allways buy the plastic bezel plastic frame and install that first to ensure a proper fit.
One more trick that i use on stubborn fits is a product called GLUE DOTS from your local Arts and Crafts (Michaels) or whatever. That works great and allows for re-entry if you mess up the first time. Never use Crazy Glue or Gorrila Glue.
The Cell Phone Surgeon