Good morning,
Not able to see what the prints will look like, I can only offer a thought or two.

First of all, I have done a few poster images, one 5.5 feet tall.
The situation called for aligning the panels the same way you would put up wall paper which had flowers or leaves or a pattern.
You have to be very meticulous in aligning the edges so the pattern matches when a person sees it from a reasonable distance.

That having been said, and trying to envision your situation, the only idea that comes to mind, is to print one panel twice, and trim and paste, locating your cut in a more suitable location.
Fred

Sorry I cannot see it, but "Misses the tiniest bit from the edge" might be too much or not enough overspray, which is adjustable in the driver.
I can't tell if "Misses" means a white sliver, or missing some that had too much overspray  and lost part of a letter?
You can turn Overspray on ot off from withing Qimage but the amounty of oversrpay is controlled from the driver.
Fred