Were you shooting offhand or using a rest?
Can you shoot good groups at 100 yards with other rifles?
If you shot good groups consistently at 50 yards the scope should be fine. Is your bullet weight compatible with your rifling twist? This would only matter if you were shooting real heavy or real light bullets.
No offense but I am suspicious of the shooter
You do realize that your 50 yard group size would at least double at 100 yards.