I agree, hard to answer without seeing the fabric.
I've added fabrics of the same color as the background, it's really hard to match the color close enough so it doesn't look chensy.
Another thought is to use the challange opportunity to get creative. Maybe add some borders to get the block up to the correct size. Sounds like you like things lined up very orderly. I'm usually the person in the line who is out of order. I'm comfortable with things being crocked and making it a design statement.