I make templates out of old file folders. I trace the template on tissue paper then glue it to the cardboard file folder and cut it out carefully. I usually make a couple of the same template if I'm going to use it a lot, just marking the corner seam allowances with a dot and labeling the template. When I use it to cut, I place a ruler along the cutting edge of the template so I don't slice my template. Hope this makes sense. It's a few extra steps but some patterns call for templates and I haven't found an easier way to do it. Maybe you could use your mylar templates but put a ruler on top of it for cutting to save the edges of the template?