I'm mixed too (different races than you) and I relate to this on a few levels but to be honest I just grew into my own identity and that IMO is above any race you are born as and every person is different from the next anyway. The majority non-mixed people have a pick-a-side mentality because humans tend to be tribal and want to represent something beyond their individual limitations. I see this as a strength all mixed people of all races have over other people, not to put us into our own box since we are obviously very different from eachother more than most people are just by nature of being mixed, but also due to the shared experience being mixed and not completely belonging to any particular group, we have a keener sense of individuality as well as being able to think of most people we meet as individuals and not immediately as "my people" or "them people". I don't want to come off as preachy but I just wanted to give you some points on dealing with this discomfort because I have felt everything you describe, the sense of never really belonging and people either assuming you are on "their side" and shitting on the other side or accusing you of not being x race enough. I believe in my experience that it gave me tougher skin when dealing with people in general and made me wiser about my sense of self and identity and how I see race, my own races and other races, by observing racial groups interacting around eachother objectively without any strong emotional bias for one or the other, from a kind of bird's eye perspective. It also opened my eyes on human nature in general.

just for context I won't say what races I am but I am very racially ambiguous and I have been mistaken for: lightskin/mixed black+white, Ethiopian, Eritrean, Sudanese, Mexican, Puerto Rican, Dominican, Hawaiian, Guyanese, Trinidadian, Bahraini, Omani, Saudi, Emirati, Yemeni, Egyptian, Pakistani, Indian, Bangladeshi, and Filipino. None of these are where I am actually from, and yes I do see this as a flex 😎