When I first started quilting I learned a test for accurate piecing that has helped me. All fabrics have a bit different thickness, so the scant 1/4 " or 1/4 inch could work depending on the fabric. It sort of drives me crazy, but I can come up short on a basic 8 inch block with not that many piecing because my seams were a bit fat.
The test is: cut three strips 1.5 inches by 3.5 inches, then sew the two seams to put them together. After you press the seams, you should have a piece 3.5 inches wide by 3.5 inches. Then you know your seam width is accurate for the fabrics you are sewing to together.
Hope that might helps, if they are picky at the block exchange.
