Trapezoid

The Hubs is knocked out; we think he's coming down with the flu (oink oink? No, not that flu, just the regular kind). So, while he's upstairs either sneezing or snoozing, I'm fiddling downstairs trying to get the apartment in shape for our guests (read: I'm cleaning).

But here's a problem, and I need a bit of input trying to solve it.

Heron is--drum roll--sewn together and has a left and a right button band. It's still missing lower arms and The Problematic Collar. The instructions for the latter read: CO, then increase at the beginning of each row for 16 rows, then knit in pattern until the collar is three inches wide. And then sew the collar to the cardigan.

After pondering for a minute to simply pick up stitches and knit a rectangular collar without increases, I decided to stick with the instructions. Having worked increases over just 12 rows (not 16), my collar already measures three inches and looks like this:

What puzzles me is not the width issue but how to sew the collar to the neckline. The collar obviously has the shape of a trapezoid (or trapezium, British English; or trapeze, Melanie English), and I'm wondering exactly which edge to sew to the neckline: the short CO edge with the two "wings" or the long BO edge. (???) The picture in the pattern is of no help whatsoever, since here the collar looks like a rectangle and not a trapezoid:

What to do? If I can't figure this one out, I'll revert to Plan A and pick up stitches and knit my own version...

This is what Heron looks like now:

I wish I had time to finish it today... but no. Cleaning comes first. Knitting will have to wait (I might have time to get three buttons, though).

Happy Halloween!