If you are shooting 3" groups at 20 yards all this tells you is that your arrows, without broadheads, group 3" at 20 yards. It tells you nothing about how your arrow is leaving the bow. The straighter an arrow leaves the bow the quicker it recoveres from any flex or misques on your part. This means greater speed retention because the fletching has less work to do to straighten the arrow out. This converts into more retained energy down range as all the arrow's momentum is directly behind the head.

If you have a badly tuned bow and you start screwing on some blades you often have no idea of where they are going to go. If the bow is tuned you can usually assume they will fly where you shot them. Notice I didn't say aim. Many people think they have to see the arrow go so they know where it is going to hit. The best shots you ever make will just "happen" and you'll not see the arrow go. You are new to archery so have a lot to learn. Most times what you need to learn will never come from a guy that just bowhunts. You need to pick up a couple books written by Larry Wise, or Bernie Perrilite. Learn how to shoot good form and tune your equipment and it's possible by the end of the summer you will no longer consider that 30 yards very long.