I'd suggest clamping the panzer in the so that only an 1/8" or so is exposed to avoid cutting the side/topsheet and only portion near the edge. Starting tip to tail with very light pressure, pull the guide and file towards you and count strokes and see how it cuts and streams off. Gradually add pressure if necessary and stop just after starting to cut into the edge and clean up. You might also follow the panzer with a coarse and finer file to smooth out and rough areas on the sidewall.
Here's a couple images to help see things, though not specific to your guide and question from our Edges
page (under construction):