What I would do is pin and glue-baste the seams before sewing. Place on ironing board, stick a pin straight down through the intersections on each piece, add a small dot of Elmer's washable white school glue in the seam allowance, press with iron to dry the glue, remove pin. This has been the most accurate way I have found to match seams and, with no pins in the way, it's easy to sew.