The number refers to the amount of deflection with a 2# weight hung from the center of the arrow when put between 28" centers.
The higher the number,the more the deflection,meaning weaker.
Too stiff is not your reason for 50 yard groups opening at this point.You aren't THAT stiff.Plus,you most likely still have form and technique issues.But don't worry,50 is a long way and you are new.