Step 3: Trimming the collar
Now you have... a really lazy cardigan! You could pop this on now and call it good, but the crafting gods would frown and possibly smite you. Instead, we'll want to prep it for it's drapeyness. If you remember from the vest tutorial, those fancy draping vests are nothing but a rectangle that extends out from the cardigan.
To make your shirt ready for that, we're going to need to drop the neckline. Draw an invisible line from the underarm of your shirt to the center. This is how far your neckline needs to go down. Mark a gentle curve upwards to meet the shoulder neckline, and cut that excess off, like shown.