You should start out with maybe 1cc and go from there. You do not want to overdo too much filler in the lips. It also depends on the look you are going for too. You can always add more filler to the lips if needed. Just remember if you are going to do your lips and you do not want to bruise you should not take any aspirins or anything that will thin the blood since brusing can occur
Given that you are starting with very full lips, there is a challenge to using fillers for asymmetry corrections. It is possible that a combination of lip reduction and lip augmentation could provide you with improved symmetry, without increasing the overall size of your lips.
Lip Augmentation will help correct your lips in a safe and effective way. Juvederm, Restylane, Belotero, are all products that are safe and effective in skilled hands to make your lips even. Best, Dr. Green