your seam can be exactly 1/4" but it can be smaller because of the size of the thread. if the thread is thick-ish and you fold over your fabric, space is taken up by the thread. make sense? you could try using a finer thread and/or sew a scant 1/4". practice with 3 1.5" strips sewn together. sew and press as usual. then measure the center strip... it should be exactly 1". some machines have the capability of moving the needle over a little. good luck for a successful finish. And welcome to the QB.