Good Morning Vicki. If you are a newbie, I would suggest you avoid this block. Take a close look at the bottom seam and you will see it curve. The lower blue HSTs is definitely kinked. If you wanted to make just one block, I would make it using PPing. Cut the center diagonal section into one piece and then do what is on each side as a separate unit. Not sure if that would work, but you get much more accurate piecing with PP.
I drew the block on EQ7. The block is in 5 sections so I don't know how she made a 12" block. It naturally is a 10" block. Here is my drawing along with how to do one with using PPing technique.