Saberbabe,
When I was young, I thought it was nervousness about the shot, performance anxiety of sorts.... As I've grown as a hunter, I've realized that the "nerves" is nothing more than adrenaline pumping. Its the sub-conscience, meta-physical, spiritual energizing of your body to do battle with your prey. We may not chase down and man-handle our prey like a lioness or cougar, but we are no different in the fact that we are predators, partaking of our God-given spiritual connection to our prey. To deny this connection and only partake of the flesh and nourishment is to malnourish the soul.
Be it by claws and fangsor by arrow or bullet, that connection will always be there. The "nerves" as so many people call them, is the physical manifestation of that connection. Like so many others here, the day that connection fails to show itself, will be the day I hang up my "fangs".
Now with the mello-dramatic and poetic out of the way.... Just remember to breath, and trust your equipment and "training"....

No one can tell you how to deal with the nerves, its something that each hunter or huntress must confront and overcome on their own. If anything goes wrong you can always blame Eddie for teaching ya wrong...