The proper term is American.

everybody born in the american continent is technically “american” too

The implied context of your question is in English.. In the English-speaking world, there is no American continent. People from North America are North Americans; people from South America are South Americans. People from the United States of America are American. There is no ambiguity. There is also no good term to collectively describe everyone from the Americas but there’s also rarely any need to discuss that.

I consider terms such as “USonian” and whatnot to be highly offensive. Nobody should tell a people what they are allowed to call themselves in their own language just because the same word means something else in another language. It would be like telling French people they’re not allowed to call their arm a bras because it refers to an article of clothing in English. Other languages where America means something else already have their own terms for people from the US. English, however, has no real ambiguity except that caused by those trying to shame Americans for calling themselves Americans.