In English, the correct demonym for a citizen of the United States of America is "American". There have been others that somewhat are accepted but are not universal like "Yankee" which half the population would take great offense to.

It isn't centering the world on us to call ourselves Americans, it's the only thing that works in the language and is accepted by everyone it applies to. Call a Canadian an "american" and watch how quickly they correct you.

I've seen people propose "United statesian" but there 2 problems with that, first it does not flow well in English, second that doesn't actually fix the problem since there's still be ambiguity with people living in the United Mexican States.