Part of our journey is learning to recover from mistakes. This one I think you can just work around as you finish the piece; especially if you use the amazing out-of-square hiding overlay doors and drawers. ;-)
Seriously, I would move along after giving this a bit of attempted recovery and call it good. I do complex glue ups in stages and then assemble the sub-assemblies for just this reason. Also, you will find plently of versions of checking for square after the clamps are on and adjusting accordingly. Our craft is one of constant learning.
"A hen is only an egg's way of making another egg".
– Samuel Butler