I have extra bone in my head skull bump like a bone tumor?

Unlikely: Bone cancer is rare, so it is likely not a cancer right out of the gate. Where is this lump, behind the ear? If so, it's likely normal anatomy (mastoid process). No skull is completely without irregularities, if you have symptoms such as pain, headaches, or increase in size would get it checked out, if not there's probably nothing to worry about.