If I were you, I'd measure my panel and then figure out what kind of strip borders (that's what's shown) I'd like around it. (You could approximate those in the photo or do something quite different.) Then measure the panel with those strip borders attached.
Next, you need to know how large you would like the resulting quilt to be. The difference between your measurement of the panel-with-borders-attached and the size you want the quilt to be is the area you need to focus on.
You can fill this area with any combination of log cabin (or other) blocks and/or strip borders.
Good luck! And please post a picture of the quilt when it's done!