It's not uncommon at all for this to happen. It doesn't mean that the designer designed it wrong or that you built it wrong. It just means that the guess about the angle needed for a particular CG point was a little out.

Every model has a specific CG that will result in the elevator and stabilizer being level. But not everyone is happy flying at the same CG or perhaps at the CG placement that results in a level elevator. We tune our models to suit ourselves and that can often result in the CG being put where it makes the model perform to suit how we fly. And since the elevator trim position relates to these other things it's not uncommon at all to find that your elevator isn't lined up with the stabilizer. If you really wish to go to the trouble you could alter the angular setting of the stabilizer OR the wing to bring the elevator and stabilizer into line but most don't bother. And besides, other than possibly on a patterm model it doesn't mean anything other than from an aesthetic viewpoint. If you modify the tail a time or two to line them up then it'll still fly the same.