Screen replacement - Now black screen with light around the edges

This is very weird, I've never seen a screen display like that before.

Were the 3 phillips head screws used to keep the metal cover sit on top of the 3 display connectors (LCD + Digitizer + Front Camera assembly ribbon cables) put into the correct screw holes?

Because if a longer or the demagnetized screw is put into the lower two screw holes there may be long screw damage that may have caused this issue.

Well I don't think it's a backlight issue because the phone is actually displaying something to the screen in that photo.

Below is just assumptions judging from the symptoms you described, so take it with a grain of salt as others may be better in assisting you in this situation:

I think it's an issue with either probably the LCD connector on the board, display circuit on the board (in this case components like filters, capacitors that are part of the display circuit? or at worse case LCD display chip maybe?).