“Telling” your counselor to mention that the AP physics class is the hardest at school isn’t likely to work out in your favor.
Your grades are your responsibility. AP classes are meant to be college-level courses. Sounds to me like your teacher is trying to prepare her students for the rigor of college courses. Have you considered that maybe physics is just really hard for you? Sometimes, despite your best efforts, you don’t do as well as you hoped to in a class.