i had problems fitting the MPI3508 screen too. I written something about this display in: https://www.sudomod.com/forum/viewtopic ... 242#p51467 (power usage fix for +25% battery runtime is included).
Conclusion: You have to cut the white plastic on the side with the ribbon cable too, to make it fit.
I would recommend the following procedure: Remove the metal backside, then remove a mm or two of the white plastic on the ribbon side (the side with the backlight leds).
BUT: Be careful, dont bend the ribbon cable too much, dont cut into it.
And dont apply pressure, when you insert this into the case, or you have to repair it: https://www.sudomod.com/forum/viewtopic.php?f=53&t=4831.
Take your time and good luck!