Wow, Izy, that looks great!! When I did my first OBW, I played with the design for a week, until I was sick of looking at it and just started sewing! LOL. I did find that it helps to take a photo of each layout. The photo will show the "stand-outs" more than the naked eye can see. But remember, it's not bad to have a couple of "stand-outs" to create movement and interest. Oddly enough, after the first OBW, I haven't agonized over the layout. I just put them down, maybe move them around for a day or so and that's it. Of course it could be I've gotten better at choosing better fabric too! LOL Can't wait to see the finished product.
PS, If you want to make it bigger, you can always put the panel in the middle with the OBW's around it in a frame. And the frame doesn't have to be regular, it can be irregular and even jagged on one or more sides. Just a thought.
Hugs and prayers for you and John.