As you can see from the design (below), I decided to make the grey corners larger. The reason I did that is that the maroon fabric was going to overpower the tiny grey print. Now that I can see the finished center, I'm very glad I made that adjustment.
And now to share the lesson I learned with this one: If I had it to do over, I'd have put a lattice around the snowball blocks. As it sits now, it actually looks more like grey diamonds as a design. An inch-wide lattice would have interrupted the connections between the blocks and given more definition.