From the picture, it appears that you have a weakness of the muscles that pull your lower lip down and this results in the crocked smile that you have. There can be many reasons for this but usually it is the result of an injury at some point to the nerve that makes those muscles work. Unfortunately, there is very little that can be done to correct this. Some people will try Botox on the other side to see if you can get a little better balance.I hope that helps. Best regards.
