It all depends on the context. People have associated the word "norteamericano" more with the prominent American culture initially in the past than geographically. The term "Norteño" has been used by a local girl to refer to another girl who came from the States to visit her grandma in a film, and the term relates intuitively to someone from the north by the denotation. Of course, we should watch out for the underlying tone as with the word "gringo". On the other hand, do Mexicans identify themselves as North Americans?

A veces entendemos 'norteamericano' como alguien de los Estados Unidos, pero se refiere principalmente a alguien de algún lugar en Norte América. El gentilicio más apropiado para referirse a alguien de tu país en español es 'estadounidense'.

Hi, Adam! The simple answers is: yes, in Spanish, specifically in Mexico (where I am from) we often use "norteamericano" for people from USA only, and Canadiense for people from Canada. As Marcos and joseph said, in a deeper level, your answer is so much more difficult to answer. It depends on what we are taught at school and our self perspective. In Mexico we learn there is only one America, the whole continent. Therefore all people living in the continent of America are Americanos, though we don't introduce ourselves as "americanos". Never.

You can say in Spanish “Yo soy estadounidense” and that means I’m from United States only

It depends on the region and the speaker. In South America it means anyone from the North. In other Spanish-speaking countries, it means anyone from the US. United States has never identified itself with a demonym, although some suggestions as US-American, United Statesian, Unisian, or Usonian have been proposed, they never caught on in the general sense. The true definition of North American is anyone north of the equator, but hardly anyone uses it in that sense.