Sometimes trying to get a smooth backstitch on soft fabric, or in a place where you have a bulky seam join can be a little tricky. Have you ever tried a “reverse” backstitch?
Start by stitching toward the beginning of your seam; this means the fabric is behind the presser foot and the raw edge of the seamline is on the left side of the presser foot instead of the right. Stitch toward the “beginning” of your seam. You may need to stop a little short of the end to avoid pushing the fabric down into the hole in the throat plate.
Turn your fabric around so it is facing the “normal” direction, and proceed with stitching. Hope that helps get you out of some sticky situations. 😉