Gay, I can't tell for certain from your photo, but it looks like you cut your white HSTs the same size as your blue ones... they are supposed to be smaller. You cut the blue from a 5" charm square, cut diagonally. The white ones are supposed to be cut from a 4.25" square. Is that what you did or did you start with a 5" square for both?
http://www.modabakeshop.com/2010/10/...ker-quilt.html
I read this pattern and fear they cut the 3 strip units too short. My measurements were the same as ManiacQ2 so decided to test it out, and found that if the strips were cut longer at 6-1/2" you could get a 9" square. This is what I ended up with.
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Just goes to show one should test first.