I saw the three rules of quilting just the other day. One of them was: DON'T TELL ANYONE WHERE YOUR MISTAKES ARE. And I see you have already found this.
I really cannot find the difference in fabric, and I looked where you told me to. I looked hard!
Your quilt is wonderful. I need one like that for my new great-grandson. This is the pattern I will use. I found the I SPY fabric at Missouri Star. It was a deal-of-the-day more than a year ago, and I haven't used it yet. But I'm sure they have that layer cake in their store.