I use to have the same problem until I bought a Guidelines 4 Quilting Prep Tool. You place it to the right, under your needle, and they sell Seam Guides inexpensively, and you put a Seam Guide down along the right side of the Prep Tool and it gives you an accurate 'scant 1/4" seam". My sewing has been right on ever since I bought the Prep Tool a few years ago. I suggest you invest in one. It's not expensive.