My bucket was not level with my wheels either.
Careful checking, spirit level and measuring tape as tools I discovered that the cause was an elongated bolt hole (loose bolt) where the loader sub frame attached to to the actual tractor frame.
The minor oval-ed bolt hole (maybe 1/8" or less) multiplied by the distances (heights) made for a considerable misalignment at the cutting edge of the bucket.
While drilling an over sized hole and o/s bolt was the real solution, I simply welded as I can always grind away the weld if need be.
Might that be your problem as well?
I say that as from the pic shown I don't really see warping of the bucket.
A moral to this is check all attachment bolts from time to time!
From your posted pic, you have the same bucket design as mine and that is one tough bucket, for shure not a manure bucket!
I know as mine gets used more like a bobcat than a farm tractor.
Also I have a tooth bar installed and dig in tough dirt as well as move or roll many big rocks.