I do things like that. I keep a supply on hand so if I don't want it pieced I get some more out and use it for something else, or sometimes I zigzag it back together. We are all human, and shouldn't beat ourselves up for stuff like this. The end result will be great.

I almost always cut the batting by an inch too short just to try to be frugal but end up fixing it.
I think you had a moment of no thinking.

Yes, that makes me smile. I have done it so many times that I now don't cut the batting till I have it glued. I make throws and use Queen size batting because I can get two throws for one package.

Oops, happen to the best of us!

It's still a good save. Not a problem just and excitable moment.

Dumb, no, not at all. Distracted, maybe. I'm gradually learning to walk away after the first mistake, because if I don't there will follow ten more. If you zigzag the batting together you will never know it after it is quilted.

Haven't done that exactly but I've cut backing fabric & sewed it together the very same way. Made me feel like the village idiot.

You must be my long-lost twin sister. :D

Ha ha. Yes it is. :-) I have loads of time to get the quilting done. I want to really take my time and do a good job.

It is always a good day when an 'goof up' is so easy to fix. I probably wouldn't start with a new batt but maybe use this as a new learning experience. Why not baste (whatever method you use) the top, 1/2 batting and backing and quilt 1/2 the quilt and then piece in the second half of the batting and proceed to finish it. It would cut down on the bulk as you FMQ. Ann Pederson calls the process quilting large projects on a small machine. Works well.