Without seeing you shoot I'm making a guess.

It could be in your grip. Some bows will require a very loose grip and some will require a tighter grip. You may also find that a tighter grip will keep your bow arm more stable (never stangle the bow though). You'l probably have to experiment a little.

On the impact of the arrow my guess is that it is in your release and possible tension in your fingers along with a possible pluck. Use as much back tension as you can and pull through the string. (easier said tehn done).

If you are just starting through don't worry about bare shaft tuning. Just shoot and get your form down. You can only tune as well as you can shoot.