Common crochet mistakes
Most changing-width rows come from an unworked edge stitch or a turning chain counted differently from the pattern.
Work the technique
Count the tops in the last correct row. Trace both edges forward. If the chain does not count, work the first actual stitch; if it counts, skip that stitch and work the top of the chain at the far end.
Try it on a sample
Make 15 sc with ch1 not counted for six rows. Mark the first and last sc and check that the row stays at 15.
Check and recover
Unravel to the first wrong row and remake it. A shorter hook loop does not fix a missing stitch; the count must be repaired.