You primarily need patience. If you have only been shooting for 3 weeks, then pie-plate groups at 20 yds is pretty doggone good.

In my opinion, you don't need to be shooting at 20 yds yet. You still need to be working on form and consistency, not accuracy. Your shooting muscles are still building up, and you are still establishing your form. Get close, work on consistency. Tight groups come from shooting the exact same way every time. When you can hit the same spot every time (regardless if it's high, low, left, or right) you have your consistency down and it's time to work on accuracy. Start close, work your way back. If you start getting sloppy groups, move closer again.

A few things that will affect your grouping even when your form is good and you are shooting consistently:

Mis-matched arrows--the arrows have to be the same spine, same length, and have the same point weight to fly the same.

Wrong spine arrows--if your arrows aren't matched to your bow, you won't get good flight, and this can affect accuracy.

Nocks too tight--if your nocks are snapping onto the string too tightly, no amount of tuning will get you good arrow flight.

Nock point too high/low--this can also bugger arrow flight.

Torque--if you are torquing the bow and/or string, this will cause problems. A sure give-away to torquing the string is a sore and/or calloused ring finger. If you have this problem, concentrate on pulling more with your first and middle finger. The ring finger should have the least pressure on it. Don't put a white knuckle death grip on the bow--this can also cause you to torque.

Follow-through--exaggerate your follow-through. Hold your bow arm and release arm still at least until the arrow hits the target. Also, continue to concentrate on the spot until the arrow gets there.

Hope this helps.

Chad