I have a tool that you can use to make any size scallops. It is a template plastic material that has moving parts to get the different sizes. I use it a lot for things other than borders. Anytime I want a curve in quilting that does the job. This also works well for figuring out the corners which I always curve as well.
I mark the curves on my border first and then sew around close to the markings to stabilize the edges. By stitching also I don't have to worry about the markings rubbing off. Then I quilt using the stitching as a guideline for where my quilting goes. After it is quilted I trim the edges close to the stitching. Then I put the binding on like I put regular binding on except you will need to use a bias binding to go around the curves. The in point of the curve will also fall into place nicely with a bias binding. I love curved edges.