If it doesn’t come clean, its entirely possible to put on a new band… fiddly, but worthwhile. I remember reading a good thread about this only days ago but can’t find it. However, I did just find an earlier one which covers it -
Unpicking upwards from the bottom edge has to be done a stitch at a time. It doesn’t just unravel easily as it does when going from the top. You need to do it stitch by stitch. I’ve done it on a ribbed cuff and on garter stitch, and also on stockinette, and it was fiddly for all of them.
I fixed the sleeves of a baby cardigan just the other night… not as big a job as your’s but the same principle. I finished knitting them, only to find the garter stitch cuffs were 2 rows longer on one than the other. (The lesson learned was NEVER knit with a splitting headache!)
At first I tried just unpicking from the cast-on edge, stitch by stitch, but soon realised I’d be there forever. So I inserted a lifeline a few rows up - I used a finer knitting needle but on a longer row I think a yarn lifeline (in a contrasting colour so you can see it easily) is the way to go. Then cut off the knitting below the lifeline, and after that take a deep breath, make yourself comfortable (because you’ll be there for a while!) and unpick the stitches individually up to the lifeline. Then you can thread your needle into the stitches held on the lifeline, and reknit the ribbing. The knitting won’t look any different going in the opposite direction as it does going up.
Oh, one thing I’ve noticed each time I’ve done this is that somehow one stitch seems to disappear from the end of the row, so increase just one stitch.