no you need both 3.5 and instead of 3 7/8 I cut 4 inches. the 4 inches you need to cut 3 each of two fabrics to make 6 triangle squares.
you need 8 3 1/2 inch squares to make the flying geese units (4).
Does that help?
ann
ps. I found the directions confusing so I basically cut out what works for me.