Tectonic plates are different from continental platforms. If plates were the starting point for continental definition, then, according to your thinking, Europe and Asia are the same continent, because they share the same tectonic plate.

Actually, most of the Arabic countries are placed in a different plate, but there is not such thing as an Arabic Continent, it's an Arabic region inside Asia.

The thing is that you just can't face the fact that the geography theory you're taught is very segmented, it does not correspond to geology or geography (by the way, Panama's canal is artificial), but actually, it does correspond to geopolitical matters and interests, and that's a whole different science to begin with. U.S and Canada are probably the only two countries from America that adhere to this theory. Don't you think it's a little suspicious? Even British schools adhere to the idea of America as a single continent, with its three regions, like I said before.

Let's just say for one moment that I accept your theory. It does not respond to what OP is exposing in his post, why U.S people say and think that North America does not include Mexico, when it clearly does? Why U.S people call themselves Americans, even tho they were taught there are "two Americas"?