Okay you have a 7-1/2" block but how big is the sashing? How many blocks did you use? I can do a project in EQ and give you the exact size you need. I usually cut the corner triangles only once on the diagonal. Less waste. and you cut 2 squares for 4 corner triangles. Let me know and I will get that out to you!
http://www.mccallsquilting.com/conte...s_On_Point.pdf
http://quiltville.com/onpointmath.shtml
Luann in CT