You sew a smooth curve, turn the piece right side out, and find a puckered edge. The stitches may be accurate. The problem can be the seam allowance trying to occupy a shape it cannot reach without spreading or losing some bulk.
Seamwork’s curved-seam tutorial distinguishes clipping inward curves from notching outward curves. Both operations affect the allowance beside the seam; neither is an invitation to cut through the seam itself.
Give an inward curve room to open
Imagine the neckline of a faced garment. When the allowance turns, its shorter outer edge needs room to spread. Small clips towards the stitching let sections open. Use the tips of sharp scissors and stop short of the stitching, following the pattern’s instructions for that fabric and construction.
Remove bulk around an outward curve
At a rounded collar tip or curved pocket edge, allowance can bunch when turned inside. Small wedge-shaped notches remove some of that excess. A notch is therefore different from a straight clip: it takes material away rather than merely opening a slit.
Try both on scrap pieces first. Draw a shallow concave curve on one sample and a convex curve on another. Sew, turn and observe before cutting. Then make the appropriate cuts gradually and compare the result. You can see the purpose without risking the garment.
Tight curves need particular care, but cutting more deeply is not automatically better. Loose weaves, delicate fabrics and narrow allowances can be weakened easily. A pattern may specify reinforcement, grading or a different sequence before clipping.
Finish by turning gently and pressing with a suitable temperature and pressing aid. Do not use the iron to force an allowance that still cannot lie comfortably. The goal is a clean curve supported by intact stitches, not a collection of invisible cuts made as close as possible to failure.