I can see why he may have not centred the window. If you push the tiles to the left (in your head) to get it looking fancy, you'll see a small gap appears on the far left tiles, push them right from what they are to centre the window and you get a small cut either side the window. The two symmetrical options around the window don't give good cuts either side of the walls. I think. (I've been playing with photo shop on it lol).
you should have stripped out tiles and done the border properly!! this has happened to me also and its a pain in the *** but you must leave a professional job !!! plus the border is too low