Davi, I was diagnosed with Stage II/III on the floor of my mouth right side and left side of the tongue. I had one third of my tongue removed, partial jaw removal, floor of mouth rebuilt from chest tissue and radical neck dissection both sides. I had clean margins in both areas and tested negative for all lymph nodes. I did not have radiation or chemo. My entire team agreed on my treatment and that was four years ago and still cancer free.
I too would suggest another opinion. You need to have complete trust in your cancer team and their recommendation for treatment. I can't comment on a PET as I have never had one.
Good luck and take care.