Tip for others on the forum working with large format tile - covering the tile with your application tape allows you to draw on the gloss surface and precisely cut those lines - used it for outlets and the first shower tiles and worked great. you could draw on the back of the tile but when making the cuts I prefer to slowly cut from the good side to minimize any chipping. the tile by the shower valves is just temporarily setting there until I mix more mortar - just checking fit
your vinyl supplies work great for so much more than decals. a while back I needed to cut a specific size hole in some aluminum and cut a circle in 651, applied it and then just followed the vinyl as a guide