Is it a mental issue, or a physical one?? I would like to preface my comments by saying that I am have battled with premature release, short drawing, and target panic for a very long time. That being said, I have only recently begun to really conquer those problems, however it is very often a life long battle. Stay with it...YOU CAN DO IT!!
If it is a mental issue...
Practice your draw without releasing. Come to full draw, hit anchor, maintain proper back tension and alignment but DO NOT SHOOT. Feel how a proper anchor feels. Do this over and over. Prove to yourself that you control the shot, not anything else. In my own case I had to go to drastic measure and draw an arrow in my house, the result was hold the draw at anchor, or patch drywall. However you do it, prove to yourself that you and only you control when the arrow goes down range.
If it is a physical issue....
Learn about proper rotational drawing form. Moebow has some fantastic videos on YouTube. Study Terry's form clock...then study it some more. Those two men have done more for my shooting than anything else...never met either of them, but their advice and lessons here on Tradgang is pure gold. Get those bones aligned. For a long time I thought I was over bowed, however, I simply was t drawing properly. Proper drawing form places the drawing force into your back and bones, rather than solely in your arm muscles. Master a rotational draw and you will be amazed how much easier it becomes to control your shots.
I am no expert, these are things I have learned from men that I consider to be experts. I hope they help you. Hang in there, you got this!!!
Good luck,
Jake