How do I fix this cabinet squareness problem ?

[Gregory King]

Joshua: I doubt that the floor on which the cabinet is now sitting on is level. Could be a tad high near the center. Leave the cabinet alone. If you are building frameless cabinets in the future , why don't you try and install hardwood edging first.

[jack duren]

You have asked this question on several forums. If you cut the parts as square as possible and all the correct lengths then there is nothing to change.

You start altering correctly cut parts and you'll open a can of worms...

[Martin Wasner]

Throw it in a dumpster

Make it a single box.

You just eliminated a whole mess of variables.