Measuring from corner to corner you can still be out of square,,, been there done that. If you can strip the frame off and notch the posts you might be able to recover. I'd still notch the posts and use them to support the framework any way, there will be a lot of weight on the frame using just nails to support it all and notch it now would save work later. I would also be setting some more posts on the ends where there are none, you wan this to be around a long time without it sagging 'eh? m2
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