It took me 2 days of drawing this out to figure out that exact question. The key is that you need to do a inset seam (I think that is what it's called). The Amy Butler rectangles are cut 6.5" x 8.5" (the blocks finish at 14"). The green squares are cut 2.5" (finish at 2"). I forget how big I cut the purple star points, but I'll look around my notepad in my room in just a bit to see if I still have my drawings.
You sew the purple squares to the rectangles first so you have the star points before you sew the four rectangles together. I started sewing the block together with the bottom right and moved counter clockwise. You put the GREEN star to the first block at the top left, press that open, and then sew the rectangle to that, the third block (which is the bottom left) is the block where you stop 1/4" from the end of the rectangle, backstitch, and then sew the remaining seam together to close up that 1/4" space you left.
I no that I am not explaining this well at all, but if you draw it out you will understand what I'm talking about. I think this seam is called an inset seam, but maybe I'm wrong and someone can correct me on that.
Hope this helps.
Suzanne