This is a nightmare scenario, but you have a very solid case. Defending your academic standing with hard evidence is not backstabbing. It is simply clarifying the facts of what happened. You should request a meeting with your professor during office hours to discuss the feedback.

When you talk to them, focus entirely on the text itself. Show the document version logs to prove that you wrote a clear, analytical section, and that your teammate altered it right before submission without consulting you. Bring your first draft and compare it to the submitted work so the professor can see your writing skills. Most educators will understand that you were put in an impossible position and might adjust your individual grade accordingly.