You could make a buttonband at the top of the front shoulder. The number of stitches and placement of the buttonholes would depend on the gauge that you have on the neckband (this is in a rib pattern?). But I think a cleaner solution is to take out the neckband and re-knit it with a larger needle. It's even possible that the problem's not with the neckband itself but with the bind off. In that case, you need only re-do the bind off using a larger needle in your right hand or a stretchy bind off.