Do not use rail mounted levels ever....
If you are using a level you want it mounted on the scope tube, the level should be set to the reticle, not the turrets, not the flat, the reticle.
Then, address the rifle with your natural hold, in fact, snap-in with your rifle in position with no scope on it, get comfortable behind the rifle understand how that rifle feels in your should pocket so you can address it the same way every single time.
Once that feel has been established, mount the scope on the rifle and again check the reticle that it is in line with the fall of gravity. After a short period if you find the level is always off to one side or the other you can then "fix" this issue by rotating the scope.
If every time you address the rifle on the range and you see the bubble is off to one side, you can then loosen the rings and carefully rotate the scope to correct the direction of your natural. It will more than likely be super tiny, not even really noticeable
Our bodies are not straight and square, and canting a straight and square object like the rifle increases the error 10x vs the minor cant induced by our natural hold. The body on a subconscious level (get it level) will not try to move or resist the feeling. Much of this problem is done by not even thinking about it. While the shooter is distracted with other things, the body will move stuff that you never see. So how do we combat this movement, comfort, if the body is comfortable it too will ignore the hold and not fix it for you.
We do so much without even thinking about it because of repetition. Addressing the rifle in terms of hold and body position has be equally subconscious. The better it feels the easier it is to execute.