Out of square 92 3/4" in one diagonal 92 3/8" in another diagonal
How to fix this?
Either I cut the boards too narrow or the out-of-square is making this impossible.
Any help is GREATLY appreciated

 

You just found rule number 1 - measure before cutting and finishing the boards. LOL
I would square up the box first and go from there on what you can use of the boards.
I don't see any other way to do it.
Dave ----

 

You can loosen the bolts that hold the bed together (cross members) and square up the bed. You might luck out and be able to use the boards you have without having to get any new ones. Cross your fingers and get it square first.

 

The difference is 3/8", but to get it back to square, you only have to move it half of the difference, which would be 3/16".

The trick will be how to apply enough force to get it to move without leaving a mark

 

2X James. And 2X loosen bed bolts. If it were me I'd use the stake pockets. Get 2 pieces of some square steel tubing with it's O.D as close as possible to the stake pocket's I.D. Long enough to fit all the way down and leaving approx. 6" sticking out the top. Put them down in the pockets on the longer diagonal. Then use a "come along" to pull the longer diagonal to match the shorter. Note what James was referencing. As the longer diagonal becomes shorter, the shorter diagonal will become longer.
Wrap the come along around the pieces of square tubing safely. Close to the bed. Don't just put it's hooks in the ends of the tubing. That is dangerous.

 

I would loosen up the bolts and wiggle things around a bit then make sure it is square and tighten every thing back up. 3/16" of movement is very small. In the end each board on the floor will need some room for expansion. I think it just wants to be talked to lovingly.