Before i give my suggestion, I will admit to two things: being somewhat new to quilting, and I confess I am a nut about what other people will think, so I am not sure I could do this suggestion myself. I'd probably rip till the cows came home...thus, quiltncrazy, lol!!!!!!!
If you are really unhappy with the back, bc the front is very pretty, what if you covered the back with another back, and tied it instead of machining. If you don't want ties on front, just do lots of ties and bury in the batting. The front is already quilted. I don't know if this would make your quilt stiff or heavy.
I think you probably need a (((hug)) for all that work.
I hope you can do something that makes you happy with it. C