Hatsan Bullboss >25 caliber (wood stock) shooting low.

I'm asking for help with a reason or reasons my Hatsan Bull boss is shooting so low. I can have the scope maxed at height but still shoot 6 inches low 10 yards away. I just purchased it less then 2 weeks ago and shot it for the first time yesterday to receive terrible results. Is there some adjustments I could make to raise the barrel? I tightened all the screws but you would think on a $700.00 pellet gun you wouldn't have this problem. Any help would be greatly appreciated. I also have the recommended Hatsan optic that is a really well made scope and I tried different scopes with different mounts and still had same results so I know it isn't the scope so id hate to shim a scope but may have to.