It's definitely not a friction fit, the feet do all the work of holding the screen in place. The bolts on the corners shouldn't be tightened to the point that the whole assembly bends. If you loosen them so it rests on the back of the display, and then push the black feet through the holes in the X that line up with the display then you should be fine. The LCD is sitting behind a solid sheet of acrylic so it doesn't need to be mounted especially firmly.
I've never built one with a 12.1" screen but as far as I'm aware the plastic driver board mounting pads should have little push fit connectors on the end that go through the holes on the driver board.
