Those are good suggestions. Thank you for the links! Added Nonestica.
Though originally unplanned for the poll idea, i ended up using Wikipedia to see if each entry is a continent or not. It seems difficult otherwise to determine what does and what does not fit. With that, i looked up Narnia, and found no mention of a continent. The closest mention is List of places in The Chronicles of Narnia which mentions a Continental Divide.
Forgive me as i take this too seriously. :) Narnia and Boxen are described as worlds, both in description and focus. Technically, every world has a continent, right? If so, for every fictional world, we'd need to add an unnamed continent option. In some stories, however, the fact that it is a continent is integral, significant, or important to the story. I've chosen to use Wikipedia's mention of it to be the deciding factor. I have no objection to an actual poll listing them, however.
Wikipedia lists Númenor as an "Island (or continent)", but other than the parenthetical option, it is treated as an island. Furthermore, it sunk. So, i'm not sure it would qualify anyway.