Just finished 3 more miters without pinning at all.
Fold 45 with excess material under, excess laid over top of bottom border fabric - even the two out.
Iron your 45 when u are happy with it. Get good crease.
Place masking tape over 45 evenly (1/2 on ea. side).
Flip fabric (45 triangle) over to the iron crease on underside.
Use ruler & mark crease w/pencil.
Sew just past tape and drawn line. (Just to avoid sewing tape).
Cut off excess to 3/8 or 1/2" and press open.
Wanted to simplify previous directions. Friend said Quiters Visual Guide uses same 4 miters but with extra steps.
Now thread and cat hair removal.....?