Quick fix: Rip out and recast using a needle two sizes larger than your project needle for the cast-on row only, then switch back to the correct needle for row 1.
What you are seeing
The cast-on edge is stiff and the needle barely fits through stitches on row 1. In a finished garment the bottom edge pulls inward and won't stretch to fit comfortably.
Why it happens
- Pulling each cast-on stitch snug against the needle before moving on
- Tension anxiety — most knitters cast on far tighter than they knit
- Using a long-tail cast on with a very tight thumb wrap
Fix it now
- Tink back to the cast-on edge, or carefully unknit row 1 and slip stitches back.
- Switch to a needle 2 sizes larger than your project needle.
- Recast on over the larger needle, keeping each stitch relaxed before sliding it back.
- After casting on, switch immediately to your project needle for row 1.
- If the project is too far along: pick up stitches along the cast-on edge and work 3–4 rows of stretchy ribbing as a border.
Prevent it next time
- Cast on over two needles held together, then remove one — this forces each loop to be roomier.
- Use the German twisted cast on, which is naturally elastic.
- Consciously relax your thumb between each cast-on stitch.