Quick fix: Count your stitches after every row. Extra stitches almost always come from an accidental yarn over when moving yarn between knit and purl stitches.
What you are seeing
Stitch count increases each row even though you're not working any increases. The fabric may be flaring outward.
Why it happens
- Yarn wraps over the needle accidentally between stitches
- Working into the bar between stitches as well as the stitch itself
- Knitting into both legs of the same stitch
Fix it now
- Count stitches and identify which row the extra stitch appeared.
- Tink back to just before that row.
- Re-work slowly, watching yarn position at every stitch transition.
- When moving between knit and purl, bring yarn fully between needle tips — not over the right needle.
Prevent it next time
- Thread yarn between needle tips, never over
- Count stitches at the end of every row for the first 20 rows of any project
- Use a stitch counter app