I think you should just give that charm a small border. And, trim it if you have to, to size. I really doubt you'll notice it. I piece fabric together all the time. And, once you quilt it, you never really notice it. You'll know it's there. Just don't point it out. Just own whatever way you choose to fix it. And everyone else will go along with it. An I'SPY is a very forgiving quilt.