Hi Jim, a piece of sand paper will work but take a bit of time, just stick with it, rub the tile along its length, NOT from front to back or back to front. once you're happy with the finish carry on and fit the trim, make sure you have a 1-2mm gap between the tile and trim to allow grout into the joint. make sure you get all that black crap off the tiles and out of the joints BEFORE you start grouting otherwise your next post will be asking for help to get the black stains off! Just a thought but did you keep the cutter topped up with water?