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.