Great trip report and nice photos...
About your underquilt. I've found that there can't be any air gaps between the quilt and the hammock because they form cold sections. The best solution is to bite the bullet, get out of the hammock and do whatever you can to tighten the underquilt suspension. That might even mean jury-rigging supplemental suspension over the ridgeline. Just make sure it's tight to your back. Also make sure that the gathered ends of the quilt are as tight as possible (within reason) to prevent the venting of warmed air. Looking at the pictures of your rig from the side and of your feet, the ends of the quilt look too loose. When I set up my hammock/underquilt, the hammock actually lies loose in the underquilt so that when I put weight in, everything's tight.
But kudo's on getting out into the backwoods. Looks like you did everything right. Tarp and underquilt tweaks are what make this sport fun!!!