<p>Email the professor just laying out that getting into 201/3 is important as you see it for a challenging double major, and what are the chances that you might actually get frozen out. There is no way first year students should get frozen out of intro, and when you email the professor, that kind of pressure makes them often open up new sections and what not. </p>
<p>With course actions, you used to just fill out a sheet and have the prof sign it. I am not sure if it is done electronically now. 19 people seems like a long waitlist for a 24 person section, but I am sure there is a tone of jostling. Someone else here may have more experience with that.</p>