Here's my 2 cents. Make the medallion as indicated, then put on a larger rectangle with a smaller border matching the outside border on the top and bottom of the medallion. then continue as the pattern is. As long as I improvise the medallion the rest will follow.

Thanks to everyone for all of the wonderful ideas! I have much to consider now and will continue to work towards a revised pattern. Gannyrosie - I think your idea is great and am currently playing around with a few similar options. I appreciate everyone's input and delight in this learning process! Thank you all :)