It could be any, or a complete combination of those factors. First, magnum spring pellet guns are among the most difficult rifles to learn to shoot well. Second, as pointed out above, pellets very seldom group well when pushed beyond 900 ft/s. Third, many gimmicky pellets (pointed, light weight, hollow point, bbs in the nose, and the like) will spiral more readily than domed or round nosed pellets. This opens up groups. Third, magnum spring guns are very hard on scopes and can break them in just a few shots, especially if the scope is not designed for it. Fortunately, if you purchased the rifle with a scope, that scope should be designed for the double recoil that breaks many scopes. Unfortunately, the scopes that come with such airguns are among the least expensive to produce. As such, there can be a significant lack of quality control.
The first thing to do, is read up on what is known as the artillery hold. This is essential for shooting spring airguns. The second thing to do, as was mentioned in the post above, is get some heavy round nosed quality pellets. JSB Exact heavy (10.34 grain) or Crosman Premier 10.5 grain round nosed pellet are two that generally shoot well in most guns. There are exceptions, of course. Third, is to re examine the scope and see if there is anything noticeably wrong. It might do you well to look at a better magnum springer rated scope. Fourth, spring guns can shake things loose. Check the various mounting screws and make sure that they are tight.
A few years ago I started the same way and thousands later here I am.
