What type of rifle, what twist rate is the barrle,, scope, and mounts do you have? What exactly is it doing? You said you can barely hit the target, but, is the gun grouping and just won;t move where you want or is it spraying shots all over.There are countless problems that can cause this. With out knowing more about what is happening I can't really help.
here are a few things to check.
Read the scopes instructions and make sure you are adjusting it properly, and have it mounted properly, not all scopes are the same. The adjustments for windage and elevation can be different on different scopes. Usually the elevation and windage adjustments are on top and right side respectively but not always sometimes they're reversed and on some cheap scopes the windage is on the left side.
Make sure the mounts are level. Some recievers Especially Savage and Rossi have rounded receivers that don't allow flush mounting of the bases and require shimming, becuase otherwise the scope is not level and many scopes don't have enough adjustment to make up for this.
Ojn a bolt action gun, remove the bolt and with the gun on a vise, a few pillows or such will work, look through the bore and then the scope. What you see through the bore is pretty close to where the cross hairs should be in the sight picture. Try adjusting the scope until they match.
Is the receiver loose in the stock?, Grip the barrel and butt stock and twist. If there is much play the screws holing the stock to the receiver are loose, A common occurance with off the shelf guns, they don't tighten them enough at the factory. If so tighten the 2 screws under the trigger guard evenly. Or if you know a gunsmith have him do it, it can be tricky tighten 1 to much can throw things off badly.
These are a few things you can try, there are many others from the wrong bullet to gun defect to bad scope. Give me some more info and maybe i can narrow it down a bit.