Good advice so far.
If it's not an issue with level or cant, then I'd highly suspect the scope is not in line with the bore. All of these can be easily fixed at home with the right tools.
An inexpensive way is with a level (or set of levels like the Level-Level-Level) it as well as the vertical reticle instrument:
EXD ENGINEERING VERTICAL RETICLE INSTRUMENT - Brownells
Using these I can get them right on, every time. My goal is to have to never touch the windage adjustment of a scope during sight-in time. I also use the Wheeler FAT wrench and slowly torque each ring so that the torque doesn't cause the scope's level to change.
: You will, however, have a problem if your base or rings can't be adjusted for left/right position. I had a set of double dovetail bases that was waaaay
off resulting in the scope looking far left of center. Thankfully this was fixed with Burris Signature rings allowing me to recenter the scope, but I've since removed those bases from the rifle. A fixed rail or fixed bases + fixed rings could also do this if one of them is out of spec.