If it were me, I'd start by loosening that loop a bit. Keep wiggling and twisting it and you will eventually get the lower knot to slide down a strand or two on the serving it just may take a bit of blood, sweat and tears. The next problem to look at is rest contact. Check all your nocks to see if they're aligned to the cock fletch the same. If they aren't that would explain the scattergun pattern of your groups. Then papertune it. There's nothing we do in a proshop that a guy with even minimal handiman apptitude can't handle, it's not voo-doo. It's just a matter of experience, and this sounds like a perfect opportunity for you to gain some experience.