I screwed up

I'm making a cute shrug to wear with corsets for clubbing, and looking at the pattern, I thought I could combine collar B with shrug body F. Looks like the neckline for shrug body B is much larger than shrug body F, because the collar is huge. Whoops.

Can anyone explain in simple terms how to make a collar to fit a particular neckline? I've never drafted a collar before, and this thing would be so cute with one.

For those interested, I'm using Butterick B4926 (Ghost of a rose, this is the pattern I told you about that you've been using so well for months :)

Black Roses shrug

Here it is! It's made from a black poly taffeta with velvet roses, lined in cotton. I will use this to wear with corsets when I got out clubbing, or sleeveless party dresses for evening events.