I think you did a nice job and unless it is a quilt as you go, I never understand how someone can get a perfectly straight backing on a DSM--it is a huge task and quite a challenge.
I think it is nice, though. I don't see the mistakes you talk about except the crooked back (a little). Probably no one would notice if you put it on the bed so the material is straight, unless you told someone about it. (assuming you want a reversible quilt). Otherwise, the front is quite pretty...and I don't see the mess you see.