It sounds like you purchased a 60" door set for a 54" shower. I suspect that at this point it will cost somebody a bundle to redo it. 54" doorsets are not common but are available, probably not as wide a selection of styles as you might like. The other option is custom made, but again you already have something installed. You could check and see if Kohler could supply different doors, but again, I see $$$$ in this picture.