Hi Mary, maybe this link will help you...........
Without seeing how the edges of the V-neck are finished it is a little hard to say, but as jersey is a knit, I am assuming the edges are somewhat stretchy, and that the V neck length is a little too long for you and you want to fill it in?
I would sew a trim with sturdy weight first on to the fabric edges of the V neck. If the holes are large enough for a crochet hook, then you will be able to use them to cast stitches on to and to continue crocheting in the V space.
If the trim that you are using is cotton, be sure to pre-shrink it first before sewing it on, otherwise it will likely shrink more than the jersey when the garment is washed, then will not lay flat.