I think what happened was that the top was stretched when you rolled the quilt between blocks. If you think about it, the outside of a roll is going to stretch more than the inside of a roll. So, basically, you hand quilted blocks with excess fabric in the top between the blocks.
Machine quilting the sashings first would probably have eliminated this problem. In general, when you are mixing machine and hand quilting, the machine quilting is always done first because it stabilizes the layers.
I would not wash the whole thing. Instead, I would try to see if I could shrink the top enough to fit the batting better. I'd lay it out on a carpet and pin the batting/backing to the carpet, then spray water on just the sashings. Use a fan to speed drying. You could also try holding a hot iron near the sashing fabric (heat helps shrink fabric), but that would get old quickly. It looks to me as if there is too much excess fabric for this to work, but could be worth a try on just one section first to see if it has a chance.
What I would do next time is starch the top and backing before layering, spray baste the sandwich together, machine quilt the sashings, and leave the hand quilting for last. I wouldn't use a floor frame for the hand quilting; a lap hoop would do just fine.