OK first of you need to PRACTICE PRACTICE PRACTICE. No really everyone makes bad shots. If you want to shoot sitting down then just grab a chair and go out side a shoot sitting down. Then you will know just how well you can shoot sitting down. Well it sounds like you have a great spot to hunt with a lot of bucks so you should have no problem getting them in close once the rut starts going. But the main thing is you can never practice enough. I try to shoot my bow every day, and about 30 arrows per day at that. Now im not saying shoot you bow every day, shoot as much as you can. I am in college and can shoot my bow every day because i have a lot of time on my hands.
So go out there and get those big bucks. Good luck.