I’m just a little ways past you on my build. I had similar problems. I ended up just focusing on getting gaps as small as possible. Then putting the floor on really sucked, but with enough patience it eventually all fits together. There will be some flexing and a lot of swearing but you can make it work. I ended up getting the floor in on one side, screwing in place, and that helped to kind of suck it all together like a girdle working around in one direction.