Do you mean when it's in a hoop, that you're trying to make the tension tight? It's not necessary to have super tight tension, it makes it easier to maneuver the needle if it's not tight, in fact. I would just fit in as much of the border as will fit in the hoop as possible, and let it have a relaxed tension. I use one of those square PVC frames, that makes it easier to fit more of the quilt in, and to get right out to the edge.
As far as the finishing knot- when I've reached the end of the thread, I float it through the batting aways, wiggling the needle up and down between the layers to make sure the knot will have plenty of batting to catch on. Then I bring the needle up through (not at a seam), pull it a bit so that the quilt bunches slightly, make the knot right by the fabric, then cut the thread an inch or a little more away from the knot. Then you can smooth out the top of the quilt with your finger and the knot will pop inside and catch in the batting. There will be some extra thread still hanging out- poke your needle in to the side of it and slide the needle along under the top layer of fabric to pull the tail of thread inside. Over time, the tail of thread will tangle with the batting and will add extra security for your knot. HTH! :)