Does anyone have any suggestions to help remediate the following scenario?

My wife and I built a new tiled access cover for our bathtub deck to replace the cover damaged during a plumbing repair. Despite our best efforts (possibly because the floor isn't quite perfectly level), the semi-finished cover is just a hair too big for the opening. If I were working with wood, I would just sand down the edges until it fit, but this is ceramic tile that has already been attached to the backerboard.

Suggestions? For instance, can we run an edge through the tile saw to trim the tile and backerboard at the same time? Can we try to grind down the affected area with a rotary tool?

Starting over is not exactly a good option, as the tile we used was hard to find.