Help, the neckband is too small

I have just knitted a sweater for my husband. I have not stitched together the neckband as I have found out that it is toooo small. It will not go over his head. Please help. Advise what to do.

Is it just that the neckband is too tight, or is the head opening too small in general? If it’s just the neckband I’d suggest re-doing it and at least binding off a lot looser, if not working the neckband with a needle size up. If it’s the whole sweater and the head opening is too small period, I don’t know what to suggest.