Okay, probably the worst question to ask but I can't set my scope up right. I have an Ar15, flat-top, 18 in barrel and no iron sights. For the scope I have a Bushnell Banner. Yeah, I know it's not the greatest but it's all I can afford right now. Well, I mounted it and set the target out to 50 yards and nothing. I'm not even hitting the cardboard the target is mounted too. I try adjusting it every which way but nothing. What am I doing wrong?