HELP !! Need MATH help with this pattern
I am doing charity quilts for foster kids when they go to summer camp next year. A friend loaned me this pattern. I love it but I don't understand why it seems to be more complicated as drawn. I want to avoid making all those quarter triangles. The center in the block diagram is 4.5" square cut. I want to attach half square triangles on the four sides instead and then have the pieces of the dark turquoise square and green/turquoise half square triangle as sashing and the white square as a cornerstone. I have already pulled enough fabric to make this quilt. I am ready to start cutting but I just can't figure out the math. Once I know the dimension of either the white or dark turquoise size is, the rest should just fall into place. Am I correct??? THANKS !!!