The yellow alternate squares will form an arc above the yellow block on the left of the quilt. With a mirror image over the yellow block on the right of the quilt.
You will need 18 2.5 inch squares in yellow. Sew 12 of these squares together with background squares to form 6 four patches. In addition, make two 2 patches of yellow with yellow. The last two yellow squares will remain single for now. You may combine the yellow two patches together with a 4.5 inch background square to make a partial block.
If you have already made your green alternate blocks, you will be able to combine the partial yellow block with a partial green block. Notice that the center square is a four patch made with two yellow and two green squares.