Hi Norah...I too had trouble with it at first because of preconceived ideas as to how it should go. I've been thinking about your question about using synthetic fabrics and the possibility of raveling. Instead of cutting the squares 71/2" and turning under the raw edges 1/4"....what if you cut the squares 8" and turn under the raw edges 1/2" before overcasting the edges together. Once you have those turned under edges sewn together there are no raw edges left. It would be worth a try especially if you have some scraps of the synthetic fabric left from another project.
Judyjo