Re: the water coming in: is your cinch buckle under the tarp? With that 2 feet of webbing through the channel, your CB might be a ways from the hammock. I use the shortest piece of rope that I can to the CBs, not more than a few inches. If you have a max of 6" on each end between hammock and the CBs, plus 10 feet of hammock pulled tight, that would give you potentially 11 feet total needing coverage. With 13 feet of Claytor tarp, that should be fine. But with 2 ft of webbing on each end, that might be too long, maybe way too long.
I have found no need for a ridge line with the Claytor diamond tarp, plenty of coverage. Of course, if you want one it won't hurt, as long as it does not provide a path for water. Just make sure that CB is covered at least a small amount. Otherwise water may run in.
Re: Shoulder squeeze- most likely hammock stretched way too tight. Even though the Claytor is narrow, I don't find a problem with squeeze. Put a little more sag( or a lot) in the hammock, and try a diagonal lie. Or a midline lie with your feet way out to the sides. The Claytor is pretty forgiving of amount ( a lot or a little) of sag, but too tight will squeeze you.
"Hang" in there, and welcome to the dark side! Way to go starting out in a deluge! Every thing else will seem easier.