Inevitably when I sew a lining, a section of the lining slips and shows past the edge. I use pins and go slowly, but lining material tends to be slippery, especially when sewing satiny fabric to velvet.

At this point there are several choices: hope no one notices (I know it is there!!), rip out the seam and try again (horror), or hand sew it. I have found a rather useful stitch to tuck in the offending blob of material.

To fold the lining in and keep it there, it works well to alternate small stitches near the original seam, then at the top of the original fold. Keep these stitches loose for four or five repeats, then gently pull the stitches tight. The fabric folds down and is secured!

This is part of an adjustment on a purchased velvet tail coat. It was faster and more economical to get a pre-made garment, then make alterations, than to make the jacket from purchased material and a pattern. Although I would have had the same issue either way; linings and velvet always gives me fits.