OK, I am here now. Firstly, I think from memory, that the original last border/sashing round all the blocks was only a quarter inch, finished, not the half inch finished that is in between all the blocks.
That isn't what I did. I put three quarter inch sashing (with cornerstones) between my blocks, and all round them too. I assembled all of them, plus that final border round them as one complete section. I also put cornerstones on the final (what should have been narrower) border too.
I had already begun to trim my pieced tris with the ruler before I ever decided on trying to make the quilt a little larger, so they had to stay the same size, just as the blocks did. So to compensate, I made in inbetween tris a little wider - which meant that they didn't go down to a point any more, they ended up with a quarter inch across their tops. Then I tried to centre that quarter inch blunt top in the middle of my cornerstones. Some were a little off, but by that time, I was past caring.
I'm going to look for a pic for you so you can see what I mean,
I think this one will show the blunt ended in between tri.
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