For practice, try one shot, with no warm up.
Try to put yourself in a realistic hunting situation, and with no warm up, pick a spot and shoot it.
As hunting season approaches, I spend very little time shooting repeatedly. My form should already be automatic, so I`m not working on form. Instead, I switch to a one shot type of practice.
For me, even practice from heights is easy, because I can step out on my deck, and take a shot before work. When I come home, I pull my arrow, and take another shot or two.
I have found it to be a great confidence builder
when I am able to place an arrow in the kill zone of a 3-D target with no warm up.
Part of your lack of focus MAY be that you are preoccupied with the possibility of a miss or worse. Being confident is a MUST when you are shooting at an animal. ANY lingering doubt will creep into your mind and use up at least some of your shooting ability, or your ability to concentrate.
The phrase "pick a spot" is so simple sounding, but when your heart is bouncing around inside your ribcage, it is difficult to do just that.
Then add some stray thoughts and worries, and "pick a spot" is the last thing on your mind.
My advice is the same as everyone else`s.
Pick a spot, but do so with the knowledge that you have become a pretty good shot with your bow.
Know this...you are not alone. Good luck.