I think I had the same experience last summer stitching mine together. I was wqorried about running out of wire, but I ended up with plenty of extra copper wire when I was done stitching. So in hindsight, I'd suggest just snipping the too tight wires and stitching it again, a little on the loose side. As the hull all comes together, it's fairly easy to tighten it a little more as and where needed.

Savor this part of the building too - it's incredibly cool seeing how all those flat boards pull themselves into a boat shape.

   I did go thru and loosen many of the stitches but still had problems.  I then realized I had put some support under the middle when I had to leave the boat for a few days and forgot to remove it when I returned.  Consequently the boat wasn't "sagging " nearly as much as intended.  I don't understand the geometry but when the restored the sag by lowering the center support the hull opened up and pretty much accommodated the bulkheads without a lot of additional effort.  I guess there is usually  a reason behind most of the instructions - even when unstated.