is your binding not mitering correctly, the problem? or are you not squaring up before adding the binding? after quilting, lay your quilt out (the quilting process causes some distortion) line up your ruler along the side & trim all the way around- making sure you have nice 90 degree corners- then add the binding- if the binding process is the problem there are lots of tutorials---and practice finally gets that right---for years I could make 3 pretty perfect mitered binding corners...then that dog-gone 4th corner would be ...ugh! finally- after years (most of the time) I get all 4 right...every now & then though...