I've never done a collar like this on a full-size garment. I have done them only on doll sweaters. I did this much in the car on the way down to Indiana from Duluth, but when I tried it on, it was all wrong--way too wide.
So I ripped it out; went back to where I started the bound off stitches for the front neck opening, because I didn't like how the decreases looked and went higher than I did before, but it still looked too big on the needles. so I knitted one more row around adding decreases in the front and back (k2, k2tog around the back and shoulders). Then I bound it off rather tightly. Since it will be a cardigan that wasn't going to be a problem. I tried it on and now I think the neck opening is the right size, so I'll knit the collar separately and sew it on.