Why won't my screen replacement snap on to install.

Hello. I am doing a fairly large repair on An iPhone 5s. I replaced the aluminum case and the front panel. Here's the problem- I can't seem to get the screen to snap in place and unfortunately broke the screen trying. I looked up icracked's video on YouTube for this repair and followed the screen install instructions- didn't help. What seems to be the problem is something is getting in the way. I figure it Has something to do with the aluminum case or I didn't button up the electronics tight enough. Anyway, has anybody encountered this before? Any suggestions?