I tried to learn to shoot left-handed, for sitting shots from a tree stand. It just messed me up both ways, and I gave up. Others have had better success.
Aim small, miss small. Focus, pick a spot. Sounds like you're not picking a spot on a big target. I frequently shoot at arrow holes in the target to get my aiming spot small enough.
If you do better snap shooting, you may be over-bowed. You should be able to hold for a second or three without straining, while you focus on that tiny spot.