As I understand reading through the above posts ... you have a center medallion that is marked, and a border that is marked (or designed but not marked). You have not yet decided what to put in the area between the center medallion and the border ... correct??
OK ... go ahead and finish the center medallion then stop. At this point you should decide what you are going to put in the area between the medallion and the border. Don't do the border until you've quilted that middle bit. If you did this your quilt would wind up wonky/uneven ... puckers .. and who knows what other quilting monsters it will create.
When we quilt, we are pulling the sandwich together. The denser the quilting, the more your entire quilt will "shrink". Starting in the middle we will force the quilt to "shrink" evenly in all directions.
So go ahead and finish the medallion then hang the quilt a while and think about it! You'll come up with something.