Originally Posted by feline fanatic
It sounds to me like you just want to do radiating lines from a central point. So your scallop is essentally a 3/4 round circle. You want you lines to start where an element in your quilt (probably inside borders) make a 90 degree angle.
When I do radiating lines like that I use a protractor so I can space my lines evenly at certain degree intervals. I find 15 degrees work well. So line up the zero on your protractor with the point of the 90 degree angle and make a registration dot