On most corners you come up against your gunna need a pleat, and your going to need to cut away any bulk thats sitting in that pleat to allow for your corners to be as neat as possible... you have your choice of single (like a hospital corner) or double as you can see hear...
First off... when you have your sides temporary tacked in pull in the corner, try and keep the amount equal on both sides.
You need to remove as much of the unwanted fabric as possible, in an M shape.
Cut away whats not needed from first fold.
Before folding next side over...
