The premise of someone being in the wrong place is always an entertaining idea that can lead to a lot of potential humor and narrative conflict. I like the fact that you chose two really disparate subjects (calculus and dentistry), as the differences between those two subjects added a layer of ridiculousness and absurdity to the story.

It felt like there was something missing from this story. It's more of an anecdote or a vignette rather than a structured story with a setup and a payoff. While the absurdity of a dental student accidentally sitting in on a calculus class is great, with a little more setup, the payoff could be amplified. For example, if you focus on the fact that the student is wearing scrubs, and maybe have her ask multiple clarifying questions that seem in earnest (like she's genuinely trying to figure out how this topic relates to what she thinks she's there for), it can really heighten the reveal when the audience realizes she's simply in the wrong place.

Overall, I enjoyed the item as a quick little absurd vignette, but I think there's a lot of opportunity to expand this piece in order to payoff the joke better with some additional setup and narrative structure. That said, I enjoyed the read. Nice work!