"North America" is the continent the USA is on, and South America is a neighboring continent. There is no continent called "America" alone.
https://en.wikipedia.org/wiki/Continent#Number
"Continent" isn't remotely as straightforward as many may think and the teaching on what and what isn't a continent (or counted as such) varies globally.
Different models are taught in different countries.
"North America" is the continent the USA is on, and South America is a neighboring continent. There is no continent called "America" alone.