You can also try to shoot at a 5 spot target. That way the other arrows are not on your mind. I shoot very well when I don't worry about a $7 WHACK on my arrows. When I shoot a single spot I get nervous and will float arrows around. You may not be worrying about that right now but you may be seeing your flyers and getting upset.

Try to shoot no more than 5 arrows at a time. 5 - 8 sets. If you feel tired STOP.

Also drop your draw weight down to the min that the bow will go. You are not in a position to be working a 70lber right now even if you can bench a mule. The guys that shoot 5 spot shoot HEAVY arrows and slow bows. They can shoot two or three rounds with minor fatigue. As you get better give your bow a 2.5 lb increase, you have pleanty of time to get it up to "hunting" weight.

Good luck.