Sounds like you have the hard part wipped. that is seeing the deer and getting a shot. you are going to have to calm down a little, I have heard of buckfever but sheesh, take a breath.
Buy a paper target of a deer and practice placing you shot. When it is time to shoot you need to be focusing on an exact point on the deer to place the bullet. You can't just get deer in the sights and pull the triger. Like he said in the movie Patriot "aim small".
Also think about your form when shooting, aim, steady, slow squeeze on the trigger. If you are forgeting the slow squeeze and pulling to hard it can pull you way off target. Excersize: With the gun unloaded point the gun at your deer target and squeeze the trigger. Watch how easy it is to move the sights or cross hairs off the aim point. practice holding on the aim point while squeezing the trigger.
Don't get discouraged, you are getting closer to getting your deer.
1) Pratice shooting at a picture of a deer.
2) Aim small
3) squeeze the trigger slowly, when the gun fires it should take you by supprise.