Need help removing the back cover.

The front screen of my phone is completely cracked and I am following the guide to replace the screen. I cannot get the back panel off for the first step. (I know someone already asked about this, but the techniques described in that post did not work for me). When I heat up the back panel I can lift it up a bit, but not enough to get one of the blue plastic cards that came with the kit under it. I have tried heating it with the iOpener and a heat gun. Is there anything else I can try?

Any advice is greatly appreciated!