Problem: Walls out of alignment in corner of bathroom. Walls already
tiled. Corner tray placed into corner leaves gap of about 5mm between
wall and shower try for about 2 feet along one wall (the space tapers
away). Should I just pack out with grout and then silicone on top?
...or what?

If I put the tray further into wall the shower enclosure will not fit.

Suggestions appreciated.

Robert