TG - I don't know how old you are but you appear to be doing everything you need to to prepare yourself. And what you are describing is buck fever.
Everyone of us gets buck fever to some degree. That's why we hunt. For the rush it gives us. The key is learning to control it. Just last Saturday I had the biggest buck I've ever had to opportunity to shoot in my almost 45 years of hunting. This was with the bow. I was cool, calm and collected as I drew, aimed and released. About 1/2 hour later though when I was standing over him and saw how big he was I 'lost it'. I started to shake so bad, I had to sit down. I couldn't even fill out my tag for 15 mins.
What I suggest for you is to just tell yourself you can make the shot when it presents itself. Don't look at the entire animal. Try to focus on where you want to place your bullet (or arrow). Talk yourself down. Take a few deep breaths. Settle the crosshairs on your spot, relax and squeeze the trigger.
Remember - you never want that feeling to go away. You just want to control it.