I just looked in my Vogue Knitting Book (a how to book). It shows a V-neck cardigan with a basic k1, p1 type border. It just says you can do the front button bands and the edge of the neck all as one continuous piece (or two pieces and sew a seam at the back neck). Maybe that is what you have been trying to do.
I don't know if that is of any help.
I can see that if the vee was not quite pronounced that adding the border would deminish the vee so that it would not be what you intended. You kind of need to make the vee an extra 3/4 to 1" (or whatever) deeper so that when you add on the border it will fall where you had envisioned it.