I think you have to go with what is most important to you. Our DNA results show what we have inherited, but they don't tell us how we have lived our life and how we move through the world. For example, I will never understand what it is like to be a Black woman in America, even though my family has some African ancestry--I have only ever experienced the world as a white woman. I think identifying as multiracial would be appropriate in your case, if you feel it is important to acknowledge those other parts of your identify formally. But if you were raised in an African American community with African American parents and that is important to you, I wouldn't worry with changing your race on documents. We're not our DNA, in entirety. Do what feels right to you!
DNA is science but lived experiences are social science, and both are equally valid, in my opinion.
Have you thought more about it since you posted this in November? I am interested.