Don't take this the wrong way, but you may not be that good, yet. Just keep practicing. Keep your bow holding arm steady and watch your grip. You should be like a stable cannon and the arrow should be like a missle launching.
Keep practicing!
Not that I took that the wrong way, but just to clarify. I've been doing this for 20 years and practice nearly everyday. Just one of those days. Update: I'm back to normal again [8D]