I agree with the other two answers.
You are more than likely compensating one side. Typically if one side is bigger (thickness) then you are pull or pushing more weight with that one side. The reason your right lat could be wider is your hand placement causing you to extend your lat out further than your left making it wider.
A good example would be a pull up. If you want wider lats then you would want to grab the pull up bar toward the edge of the bar extending your arms out further. Or if you are doing a deadlift you would want to reach out further on both sides of the bar, extending your range. This help build Wider lats. Adversely if you are looking to building thickness you would hold the bar with your hands closer. You can lift more weight and it puts emphasize on thickness. Check your form next time. You might be reach farther out on exercises like this with your right arm while keeping your left arm in closer.
IF you want to get symmetrical you should look at doing single arm exercises. You can focus on form and making sure you are engaging the muscles correctly.