Had a nice little evening hunt today. Sat from 4 until dark. I'm set up in a tree that is about 15 yards off of a heavy used doe trail. There is a spruce pine tree between me and their trail, so I'm concealed until they get into position for the shot. At 6:15 two does came strolling down the trail. One stopped at 18 yards quartering away with her head down. I drew back, put that pin behind her shoulder and counted 1 mississippi 2 mississippi 3, and let her fly.... the result - a big fat BLAHHHH. She flintched a little. I missed her to the left. I shot to the left of her chest and under her neck. I'm sighted in dead at 20 yards on the ground, but in the tree my arrow is definately NOT going where my pin is. Should I switch to a pendulum sight? What the heck is my problem?