To get the best stay stitching, first set stitching length to 1.5 and check twice that stay stitching line is at least 1/8 away from the sewing line. Don’t pull or move fabric here and there because a simple movement can change the alignment of sewing.If your seam is not up to the mark then the finishing will be unprofessional and you won’t be able to get the desired result. Once you are done with the seam, to make it look nice and clean, always use pinking shears and cut out the revealing parts. Cut a small part first to see if the trick is working on this kind of fabric or not? See here: