This is a picture of my cat, Neko, laying on what WILL be a very large afghan for my queen sized bed. (I've abandoned the duvet cover idea, now I'm just going for a queen sized afghan). For those of you familiar with this pattern, you can probably see where I've added motifs to continue the pattern out past where the original one stopped. I didn't make my motifs any bigger, to extend this, I added motifs to the pattern.
A regular comforter for a queen sized bed is 86x86. So, my thought is to complete the square (the part inside the light blue border) and use the borders to adjust the size.
I couldn't resist one more picture of Neko. Besides, you can see a little of the detail of the motifs here.