There are a few potential causes for a reticle to appear canted.
The scope can be properly aligned but the way you are holding the rifle causing your eye to perceive the reticle as canted. Right-handed shooters shouldering a rifle commonly report a reticle appearing to be canted to the left, or counterclockwise. Left-handed shooters will generally report seeing the reticle canted to the right or clockwise. To fix this, try positioning yourself completely behind the rifle (chin aligned with the buttstock) looking through the riflescope at the reticle straight-on. This tends to eliminate that illusion created by having your head turned slightly while shouldering the rifle.
Aiming at a target or background that is uneven or shooting from an uneven ground may cause a reticle to appear canted. Shooting from leveled ground may eliminate the canted appearance. A shooter not accustomed to shooting with a bubble level tool installed on their rifle may make the mistake of believing the reticle is canted because of the way the rifle needs to be held in order for the reticle to be held level. You can verify this again by getting completely behind the rifle to confirm proper alignment.
Many shooters have a bubble level on their rifle installed on top of the turret cap, or will rest a level on top the of turret cap during optic installation to level it. This can skew your results by making the riflescope turret appear to be sitting level in relation to the rifle when it is not actually sitting level. Sometimes, the turret cap (or the fiber optic indicator on the turret cap) will sit slightly crooked and cause the bubble level to be canted slightly. Rather than using the top of the turret cap, try putting the level on the inner turret post top underneath the turret cap (or using feeler gauges on the bottom of the scope) to level the scope.