Did you do a seam allowance test? It really isn't about the *actual* seam allowance. It's what your piece measures on top after it's sewn in. Cut three strips 1.5 inches wide by about 3 or 4 inches long and sew them together on the long side. Press and then measure the center piece on the right side and if it doesn't measure 1 inch you need to adjust your seam allowance or your pressing technique.