Large gap in corner of tiled shower - Tile Advice

[Ollie_selby]

Looking for some advice of tiled my en suite and coming towards the end and gap down the edge is getting bigger as I go higher and looks as though will be about a 20mm gap
What do I do?

 

[Dave]

Hi.. did you start with a full tile from the corner ..?

 

[Tile Marble Granite]

Green board inside a shower is not ok. That shower will be leaking like no other, it is just a matter of time. Did you waterproof the niche? The gap speaking, the tiles need to be removed and reinstalled eliminating the gap.