Does the needle on your machine mone right and left. If so, usually one click io right will give you the scant 1/4 inch you need for greater accuracy. I find you can only use quarter inch seam when sewing shapes where all sides are the same measurement, otherwise have to go to scant. Suggest you so two or three samples, measuring after each sample, adjusting the width until you have the accuracy you need. I find that any time you change a piece of a different shape it is necessary to use the scant or other width to make it fit. Also check the 1/4 inch foot it might not be accurate.