When sewing needlepoint into pillows, stockings, boxes or other projects, you will normally stitch along the channel where needlepoint stitch meets empty canvas. This channel is marked by the black dashed line in the illustration, and is known as stitching "in-the-ditch."
Often, the sewing stitches will catch the needlepoint wool stitches slightly - this is normal and helps hide the ugly, unstitched canvas edges.
Using your sewing machine's zipper foot will allow you to easily stitch very close to the ridge created between the needlepoint stitches and the un-stitched areas of the canvas.