I am glad you found the problem. Those little minor details can sure baffle us.

The only thing is to check the cut or the seam allowance, but depending on how many you have done, I would go with them the way they are.

Here's the finished quilt. I can't even tell that the outer squares on the blocks are a tad smaller. Thanks for all the advice though. Now I know how to be more accurate if I need to.

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I bet it's a seam allowance issue. A couple of threads bigger on each seam adds up.