Problem with Simple Rooms Tileset

I'm using Nifflas' Simple Rooms tileset, and I can make some of the corners look nice, but not others. See the attached screenshot.

Is there some way to fix this easily? Or do I need to use a different tileset in order to avoid this problem?

Thanks!

The 2x2 grid of tiles just to the right of the 3x3 wall tiles are designed to fill in those corners.

Stick the tile I've outlined below in the space you don't like.

Perfect! Many thanks.