First, get yourself to another Doc (Oral Surgeon or ENT); maybe the first one was right and maybe he wasn't, but the stakes are too high to take a chance (and sometimes it's hard to actually see a Doc because of their schedules and typical barricades of admin and nursing staff, so the sooner the better).

While you are waiting, if there's any way for someone to take a digital photo with a camera while you are holding the mirror, with something else in the photo (even a finger) from which to judge size, do that -- Superior to memory (I've done both and the camera IS better!) -- Do it outside in sunlight if you can so the camera has a sharper picture without the flash bouncing around inside your mouth.

If it turns out that it isn't benign, for the sake of your ENT's other patients, it would be a good thing to send a copy of the pathology report to him (by registered mail if you want to get his attention; he will be then waiting for legal paperwork to follow and feeling just about the same way you are right now! Then have mercy and take him off the hook with a phone call ).