How Could I Be So Off on my Measurements??
 

I will be the first to admit I am not good in math! I'm at the point of making the sandwich. I laid out the top, then laid the backing on it just to double check everything. I'm about 12.5" too short on the backing!!! What was I thinking? Obviously not much when I cut it!

It will be Ok!!! Just piece it!!!

Sounds like a perfect opportunity to put a 12" pieced strip on the back. It'll be great!

Just piece it. It will be fine.

I do this kind of thing so often, I expect it every time. It's not a mistake, it's a design decision.

I find that I make mistakes if I am tired and stressed out. Don't worry, just add another piece. Good Luck!

Yep...happens to all of us sometimes....add another bit and go forward...it will still look good.

I only do backs two ways. Too small or way too big. I'm to the point it doesn't even phase me anymore.

Do you have any of your fabric left over from the quilt? You could make a nice border on the back!

I agree, piece it. What I generally do is to lay out the top then the backing on top. I fold this way, that way and the other way until I figure out which way it needs to be cut. When I get the folded piece figured out, I leave it all laid out as is, then grab the scissors and start cutting/slicing/ripping. Then lay it out the way I think it's supposed to go and hope for the best. Usually works with only one seam. That said, I first figure out sq. in. of fabric needed, convert to yards, add a bit and then buy and do as above.