Inkscape/Repeated Shapes

Hi - to try and avoid waste glass, I want to be able to butt shapes up together, like the image. I can sort tabs out, etc, that’s not an issue.

But no matter what I try, I can’t seem to get WAM to generate a file that only cuts that middle line once?

I’ve tried grouping objects, combing paths, all sorts of path functions, but I can’t seem to make it one total object.

If I select the nodes, it’s clear that the middle line is duplicated, but if I try and remove a node, it then takes out a corner (if that makes sense - it’s clearly still treating it as two separate paths or objects, or whatever they’re called.

I still really don’t understand vectors that well, but if I were doing this in photoshop, it would be the equivalent of flattening the layers.

I can still only do the basics in Inkscape

Can I do this somehow, it surely cannot be this difficult?