I sew the sashing strips to the sides and sew the row together. Assuming that the blocks were square and all things are reasonably even, I sew a row of sashing strips and corner blocks. Each strip is the width of the block and each corner stone the width of the sashing. I take great care when I press the rows so the corner blocks nest into the row. I pin-pin-pin and sew both rows together. Hope that helps.