First off the sweater is complete. My question-is there a way to make the sweater smaller ( the back panel is too wide) without tearing out everything???
You might be able to widen the seam a bit to take in a small amount of extra fabric. If it’s more fabric, you could sewing machine stitch along a line then cut off the excess knit fabric before seaming. Use short sts on the machine to catch all the strands and stitch up and back on the line.
This is similar to a steek.
I think I will take your first suggestion and open up the seam to remove some of the extra stitches. It is better and quicker than ripping everything out and starting over