Are you left or right-handed?
Usually your dominant arm will hang slightly lower than your non-dominant arm due to greater use/flexibility etc.
If that is not the case and there is no history of any injury,scoliosis, etc look at you daily activities to see if any of them result in postures/positions/repetitive movements that may be stressing one side more than the other. Modify these activities to eliminate the causative factor and then do some stretches and use unilateral training (DBs etc) to correct the imbalance.
Sure some postural deviations can result in further problems down the road, but don’t get too worked up over minor differences. Some people take these things way too seriously. It’s not as though you are Quasimodo or anything. As long as there aren’t other symptoms in conjunction with this finding, just follow the above advice.
Obviously you could see a chiro, PT etc to evaluate you, perform some treatment and get you started on a program to correct the problem. However, don’t buy into the 3X/wk for 6 mo crap.