Deer have a large muscle running up the 'top' of the neck. To be assured of an accurate neck shot you should aim approx half way up and half way 'through'. However a deer's head and neck is always moving and for the inexperienced is likely to result in wounding.
It is also for this reason that i would not recommend a head shot. I have trailed many dear which have been shot by the inexperienced trying head shots and resulted in blowing off lower jaws or removing ears, etc.
Until you gain more experience, i strongly recommend you reserve your shots for the 'boiler house'; the heart. Access the following link:
culling: shot placement (1)
The benefits are that even an averaged shot will result in terminal destruction of the heart and/or lungs as the target area is larger and the body moves less than the head or neck.
Take the shot, keep your eye on the scope and observe the deers reaction to the shot whilst you cycle the bolt and reload. Remain there for some minutes to ensure that the deer does not rise again.
If you shoot the heart, the deer should either lunge forward or jump before dropping. A deer that hunches up like a cat when scared is bad news - you've missed the vital and shot the stomach (rumen).