Inspect if everything is cut and if everything is flat. If it looks good, then proceed!

Don't worry about the front. Most of the times the front is still good, the cutting at the back side won't be visible when everything is in. But please check before you proceed.

Test if the screen sits flush.

Make sure that the screen fits good. There is not a lot of space in the shell. If you proceed anyway, you could damage the screen. Cut some more plastic if needed.