Brownish patch on buccal mucosa. : (.

I am not sure since when this is there, but i had a dental filling on 13th april, it was not there that time, so its after that only. So take it 15-20 days.(but i noticed it on Thursday itself). I asked a dentist friend, he said can be malignant melanoma and m scared! I have attached the image, please help me what it is! I am scared about cancer! It doesn't hurt or anything, when i lick it it feels sour and feels like if there's a crack line or cut, and it doesn't bleed, i sometimes see that there's clotted blood in dot dot pattern(1-2 max), there are no lumps too, but little distant from that bruise site i can feel a nerve pulsating (like swelled a bit), but in left side of mouth nothing is there. I am really scared.! In second picture white line marks the cut like lines i was saying, and yellow shows the clots, i don't smoke, drink or eat tobacco, haven't exposed to sun too. I am not sure if i had bit that place unconsciously. Please help me to rule out cancer! :(.