Sawdust, if you struggle with those pinwheel intersections, where 8 fabrics come together, try basting the center before you sew for real. To do this, pin as you normally would, but turn your stitch length up long, mine is a 5 for big stitches. Then just sew about 1" at the intersection, 1/2" before the intersection, through the middle, 1/2" beyond it--that's about 5-6 stitches total. Go slow, just trying to keep it all together. Take it out of the machine and check the middle. If you are happy, turn the stitch length back to normal and now sew the entire pinwheel seam from edge to edge. If you are not happy, quickly pull out those big stitches and try again.
Another tip: be sure your half square triangles are exactly 2" square, press firmly to the darker fabric, then sew the top half and bottom half of the pinwheels. Check each pair to be sure they are both 2" x 3.5". When both halves are the correct size, baste that center intersection before you sew for real. It is no fun having to rip out little stitches through all those seams--you probably know that. I call this "ruler checking your work". If each unit is not the right size when first made, it will not miraculously become the right size when you do the next step. After checking yourself on a dozen or so, at most, you'll have it down pretty well and the rest should go together faster and easier.
Good luck!