Is it the neckline on the body of the sweater or the neckband?
For the body of the sweater, knit across the given number of sts for your size 33(43, 53) in pattern stitch. Turn as you would at the end of a row and begin the cast off of 1 stitch at the neck edge in every row until you reach the stitch number for your size. Then continue to work in pattern stitch to the measurement of the back shoulder shaping (usually measured at the armhole edge).
It may be easier to decrease one stitch at the neck in every row rather than cast off especially at the end of a row.
Don’t worry about the sts remaining on the left needle when you turn. You’ll get to them in the following directions.
If this isn’t the part that’s a problem, just let us know. What is the name of the pattern?