Did you happen to use two different presser foots? I was once in the middle of a block and needed to purchase a new presser foot. The person who sold me the presser foot wasn't a quilter and sold me the 1/4" presser foot. Little did she and I know that there was a 1/4" quilting presser foot. I had mentioned that I was a quilter/piecer. When I finished the block certain portions were way smaller than others, yet I had made many already that came out perfect.
Without seeing a closer pic of the center, I can't even guess what happened there. Sorry that you're having such a difficult time. You will overcome this.