OK ... now I see what you're talking about. The border around the vintage fabric is actually one piece with red/white in the middle then green plaid, then black. And your'e fussing about the black rim around the block perhaps??
You can fix it by attaching a nice size decorative ribbon around the outside edge of the Octagon. I would suggest something with black and gold. The black will help "mask" the black border around the Octo's.