Sorry to hear about the way it went down. Sounds like you were 100% confident in your shot. Don't beat yourself up too bad. Like others have said (and you've already said), disect what happened, how to avoid the same outcome, and learn from it. Get back in a tree and hunt.
1. Don't alert the deer to your presence. I know you see this on all the hunting shows ("maaap - deer stops - perfect shot) but I'd rather wait for the deer to stop on its own. They usually do, and if they don't, oh well. Let em walk. Why put a whitetail on full alert and shoot them when they are staring at you? Your just asking for one to duck the arrow. I know better than that.
IMO this was the downfall. TV is to blame for this craze in bowhunting. I've never "stopped" a deer and never will. The only possible thing you can do is alert them. Why on earth do people continue to want to alert a deer they intend to shoot totheir presence? To each their own I guess, but I'd rather let them walk and hope for another day.