If your hitting a 3-d target as good as you say you are, but you' re missing the vitals when shooting at game, then it sounds like your not relaxing when you shoot at live game. Talk yourself through the shot just as you would when shooting at 3-d targets. Have you shot your bow since these outings at 3-d targets? Could you have knocked your sights out of whack?

Now, in my opinion, I would have tried to find the doe before shooting at the buck.
You' ll probably get a few follow-ups to this,(about shooting a deer after wounding one w/o finding it) but try to learn from this experience. No matter how well you shoot at a 3-d target, it just isn' t the same when the rush hits you and your trying to hit a live deer.