RE: Am I a total idiot?
Judging from the blood trail you marked, I believe this buck has circled back on you. It does not appear you have searched south of where the shot took place, it might be that you do not have permission to be there. If that is the case, I would talk to the land owner and see if you can take look at it. If you have today off of work, I would get back out there and check every piece of thick cover, every laydown, and every ditch in the area.
I killed a doe last year that was hit hard, great blood trail and this it just stopped. I had start to make circles when I seen her laying, she had crawled under a lay down tree top and was almost completely concealed. Also, a friend hit a buck last week with his truck, we went out in the morning and could not find it at first. This buck (with a broken back) had crawled into a ditch and crawled to a narrow spot where again the deer was almost completely hidden. The point of this is, a deer that is not hit great (one lung shot) will have the mind to hide itself in the best cover available. Get back out there and search slowly, checking every single piece of cover you can find. Good luck and keep us updated.