Here is how to achieve a nice rounded neckline every time:
Cast On all of your front neck stitches (like the boat-neck style)
Work short rows, knitting across a few more of the CO stitches each time you come to the neckline until (after a few rows) you are working all of your newly CO neckline stitches. This creates a gradual, curved neckline that can be as shallow or deep as you prefer.
Use Shadow Wrap Short Rows (SWSR) to avoid messy wrap and turn gaps along your graceful rounded neckline
This technique for neckline shaping is used in the following Cocoknits patterns: