No one is perfectly symmetrical and your kilt will always be slightly off kilter * depending on the exact shape of your hips and posture.  Occasionally, that asymmetry is noticeable or uncomfortable.  But, it can be remedied by moving the right-hip buckle and strap up or down to level the kilt.  Usually, only the right-hip buckle and strap need be adjusted, and not by much.
 
NOTE:  Lowering the right-hip buckle raises that side of the kilt, and raising the right-hip buckle lowers that side of the kilt.
 
* kilter: working order or alignment; good condition, order.  Origin unknown.