I have had this happen several times. Just a over a bit would usally fix mine. I didn't pay enough attention when I was putting it together. Always a pain to add more to the end or side but, I did it. I never mind piecing the batting or batting. As long as the top is nice and even, it will be okay.

oh sorry about this but youre heart is in the right place which all that matters

Sigh - experience is the best teacher - thanks for sharing!

Would love to see the quilt.

Can your DH make some blocks to add to the back where the missing fabric should be?
Can you add a contrasting piece of fabric?
Can you get some more of the fabric that you are going to bind the quilt with and add that?
Can you make some scrappy blocks to fill the gap?
This is an accident but I do appreciate how much more upsetting it is when it is your DH first quilt. Sorry for your distress.

I did that once too. I had JUST enough backing and miscalculated how much I rolled at the beginning. A sure enough, I ad several inches to go and no backing! Had to take it off the machine, sew on more backing, put it back on the machine - never fun- and finish up. I called it a " design decision" as I always do when I screw up!

Oh, heavens! I piece my backs all the time. It's really not a big deal, and I can almost guarantee no one will notice.

things like that happen. Add more muslin or finish up with a scrappy piece from the fabric used on the front

Would love to see a photo and I'm sure the recipient will just be so pleased!

It will look fine with more muslin added on.

But what about taking the opportunity to put the friend's name on it, and maybe a date, a wish for fast recovery, etc?