Biopsy of my tongue want cancer buy he wants to see me back in three months then possibly do another biopsy in six months...why?

Pre-cancerous?: Perhaps some suspicious, but not definitive cells. Sometimes need to follow up and see how things go one time-check that everything is benign, or not.

Followup: It is to followup to assess the cancer. Wouldn't you want to know if the cancer is entirely removed?

Needs close followup: Tongue cancer is difficult to diagnose and your doctor feels you are at risk. If you have leukoplaque there are already changes on your tongue. If you are a smoker or have other risk factors then your doctor is concerned enough to keep a close eye. Early detection is the best chance to cure.