if, as you back up using your 20 yd pin, your arrrows just keep getting further and further right without ever making a move at all back to the center, i believe that is spine. you may need to take 1.5" off those arrows. if you're getting a bit of a ')' as you back up, then your rest needs to go to the left.

now if it was me, i'd take 1.5" off the arrows anyway. and then i'd start over - but if you don't want to do that, move your rest to the left a bit, resight in from 20, and start over.

the object of the game is to be able to hit a bull at 20, and as you back up, all your arrows fall in a vertical line under the bull you were aiming at. then you'll have your center shot.

i believe the spine is correct, but maybe at 29" they may be a little weak. i'm no spine guru though.

AND DON'T LISTEN TO DOTHEAD, do your left and rights first.