well it sounds like a little anticipation on your release.if your muscles tire out easily make sure your front shoulder stays down and you put all the pressure of your bow hand in the meat section of your thumb only,not the top portion.try keeping your wrist all the way to the left on your bow hand and let the bow rest in the lower portion of the thumb area pushing only with that part of your bow hand.get a wrist strap for added security of not worring about dropping your bow.if your shoulder is in the right positon you should feel it in your traps located on the upper outside arae of your back under your arm.relax the bow hand fingers and release fingers. when pulling your bow dont put all the pressure on your front shoulder with it in the raised position for it will tire you out more quickly. just a suggestion.it will all come together with consitant form.there are days when we all shoot below our norm just remember dont keep shooting if this occurs for all it will do is add to your frustration