Go for a second opinion! Drs. Are not the end all and be all - they do make mistakes - because you are 20 they can be dismissive if oral cancer because historically it's a smokers and drinkers diagnosis and usually found in men over 40 - we have several young people here now and the face of oral cancer is changing! There are a few women here from 20 on up who do not smoke, don't or rarely drink and are HPV - (HPV + is associated with some tonsil, and base of cancers) so theres a new generation.

Do you have a sore anywhere on it? Ct scans don't always pick up microscopic cancers, and the results are only as good as the radiologist reading Them. So get a second opinion and keep pushing until you get an answer. It's likely not cancer but maybe related to your infection... Perhaps it never healed properly? But just to be on the safe side.

Good luck and let us know what happens.