A 3.5" unfinished HST is 3" finished. To make 2, you would normally cut a 4" square, sew the diagonal seams cut and trim to 3.5". So basically 8" seems correct to me for the 8 ata time versions. You should have to trim them a tiny bit. If they are too small, have you checked your 1/4" seam allowance lately? Here's a way to double check:
http://www.quiltingboard.com/tutoria...ce-t89997.html