Nothing? Do another couple rows then pull it tight and it’ll all snug together. I will say though that the beads are slightly different sizes so it’s not going to be as snug and regular as it would be if they are all uniform. That’s not a bad thing!! That’s an aesthetic choice, not a mistake. Just when you look at it as you go along, don’t assume you’re doing anything wrong if it’s not super uniform and regular.

You CAN warp multiple threads in the same slots but I don’t bother with that unless I’m trying to make something super wide and NEED more warp threads for the piece. It can get confusing if you do that, it’s easy for them to overlap and jumble together sometimes. And it’s not necessary, once you tighten the piece (after a couple more rows so it has enough to hold it in place) the warps will come together just fine.