The completed block, Whew!
Now there are only the two pieces to sew together. Pin carefully as there are four curved seam lines that will meet in this variation on this center seam. Pin them first, then the outside edges, and the straight center seam. 
When you have them together into the four rows then pin them to start joining the rows together. Once again the most important points to match up are where the curved seams meet, then where the straight seams meet, and finally the edges. 
Finish sewing all curved pieces together to make the 16 three inch squares. That is without seam allowance. Press seams towards any part you want to stand out more.
Now that the hard part is over you are on to the easiest part of assembling this block. Sewing them together into rows. Make sure you pin the places where the curved seams meet first. Sew them and make sure they look nice.
