Hi Alex – don’t panic! This is fixable.
It doesn’t look too far off and I think you’ll be alright. If worse comes to worst, send me an email through the Contact page and I’ll give you my phone number so I can help you out. I’m off to dinner now, but briefly, here’s what I propose:
Position 4R so it lines up with the floor slit and 5R, and trim the overlap between 3R and 4R as you suggested.
Instead of matching 2R to the corner on the floor, match it to the position of 3R and accommodate the difference by fudging the position of 1R and 1L as necessary. As long as they line up with each other, don’t worry too much about the marks on the floor.
You may end up with a few extra wrinkles in the tubes, but honestly I don’t think it’s going to end up being a big deal.
Cheers!
Matt