I bite my inside bottom lip sometimes, there are 2 lumps when I do that are enjoyable to chew, just a habit, doesn't hurt but I've read it causes cancer?

Chronic trauma. Chronic trauma and inflammation may predispose to excessive tissue reaction that may promote cancer, though the risk is small. More important is the possibility of the bite site getting infected and the infection spreading to other organs. You may wish to consult your dentist for a "mouth guard" that would preclude biting.
Unsure. Oral cancer is primarily started by irritation like putting tobacco in the same spot. I am not sure that chewing on your cheek is associated with cancer. The first sign of oral cancer is leukoplakia or a white plaque at the spot.