If you have a few triangles done, you can pick a random CENTER of the triangle, at least an INCH in from each side, and put a DOT (on the dull side is fine). Then draw a line to each tip of the triangle from that dot. IT NEED NOT BE IN THE CENTER. Now be sure that each sub triangle is labeled… A Light A Medium A Dark, B Light, B Medium B D C L C M C D etc.
Only cut one triangle apart at a time, so you don’t get confused..
Now you will IRON the Light triangle on to THE BACK side of the light fabric, the Medium triangle on to the back of the Medium fabric.. the Dark Triangle on to the back of the dark fabric using the shiny side against the fabric… it SHOULD stick.
I usually align the OUTER edge of the triangle with the straight grain of the fabric, less stretching….
Now go to your cutting board and Using a Ruler with a QUARTER inch marking, you will use your rotary cutter and cut 1/4″ outside the FP, giving you a very accurate seam allowance….