The majority of people are this way. Unless you make a concerted effort to use both sides of your body in everyday activities the same, symetry will be slightly off. I've been having to make sure I carry my 1 year old son equally on both arms. I usually carry him on my right side and my right arm is noticebly smaller when I flex.
Savvy observation, sir. When my children were of the carrying age I tended to carry them with my left arm. To this day my left arm is considerably smaller than my right arm HOWEVER, my left arm is noticeably stronger than my right arm. Kinda ridiculous.
To the OP - Some of us are just blessed with ridiculous symmetry. Some of us are not. Consider the study that found that women are more attracted to men (even without them knowing it) who have the most symmetry in their faces (I think I recall that Tom Brady's left and right side were around 96 percent the same). Likely you're one of the few who actually notices that you're asymmetric to any large extent. I broke a collar bone when I was 6 and the two sides of my upper half (from the breaking/healing point) couldn't be more different. Nobody notices unless I point it out. Peace, man!