And last *I* checked, the people north of the USA are Canadians, the people south are Mexicans. Those in South American have their own country/place-names, none of which are typically labeled "America(n)".
If you look at what citizens of the USA call themselves, it is Americans. That is also the way the rest of the globe typically labels us (I include myself, as I am an American). We aren't typically labeled United Statesians, or some other such nonsense.