If you hit him in the neck, and he ran for 300+ yards, I would say that you missed any major arteries, the spine and the windpipe. Severing any of those would bring him down fairly quicklike.
Did the arrow pass through? What kind of tissue was on it?
I have cut my finger before and bled like a brutal murder just occured.

A buck my brother took in gun season years back had an arrow wound in it's neck, in one side and out the other. It was healed over but looked NASTY. You may have not hit as center in the neck as you think. The arrow could have only gone slightly under the skin and out again.

In any case, keep looking. Many times a buck will circle back near the spot where he was hit and bed down and die. I would try doing the increasing size circle search both at the stand site and the last blood site. If he was heading downhill at last blood, have another guy go in that direction slowly, looking for the buck. If any prominent travel routes are going that same direction, put a guy on those trails searching.

My brother hit a buck on Saturday and the shot was downward and quartering away. We found no blood in the direction of escape. He kept searching for blood and I followed the escape route. I soon ended up on a defined trail so I kept going. Sure enough, after 100 yards or more, I found blood on that trail. I kept on it and found where the blood dropped off the trail and started downhill. I knew he was a gonner at that point and sure enough, at the bottom of the hill, there he was, belly-up. Get some fresh eyes out there to help you.

Good luck and learn from mistakes.
Bad shots, in time need lots!
Remember that....very important.
(And others shouldn't throw stones.)