Although I am new to the crossbow, I have had a lot of experience tuning and repairing compound bows. If you have access to a chronograph, shoot 10-20 crossbow arrows through the chrony and record the speed FPS for each shot. If the collective speeds of all your shots are consistent than you know your problem is the sighting device and not the crossbow.

Another way you can do this is to remove your scope and reinstall the open sights that came with the crossbow. You would have to sight-in the
open sight pin at the yardage you want to shoot. If you shootconsistently with the open sight at different yardages than you know the problem is the scope and not the bow.

I hope this helps.