You are half-korean, so what is your other half? White? So you are half korean and half white.
You wouldn't say you are 100% korean and 100% white. That would be ridiculous right? Your ethnic history and composition can't add up to 200%. Even if you claimed to be 100% korean or 100% white, neither white nor korean people would consider you to be 100% white or korean.
That's my point. There is nationality and ethnicity. Those are two different things. A chinese person could move to germany and become a german citizen or national. But nobody would consider him an ethnic german.