After you sew the five strips together using a 1/4" seam allowance you should have a square that measures 5 1/2 " on all sides. Then when sewn next to other blocks they should measure 5" square finished. If your seam allowance is accurate at 1/4" inch and you still don't get the right size the only other thing I can think of is to double check to see if your pieces were cut accurately. If you have not already cut all your pieces, you might find it easier to do as Mdegenhart suggests and sew your 5 WOF strips together then crosscut them into 5 1/2" segments.