350 sounds incredibly low. Most schools have to accept 2.5-3 applicants for every seat they'd like to fill. Georgetown is especially expensive, so my guess is that they're on the higher end of that....
That said, I'm assuming that they ultimately accept between 525-600 of the applicants they interview. I say ultimately because it sounds like only 25% of applicants are accepted post-interview, and the rest are waitlisted (some rejected) until a decision is reached later in the cycle. Update letters/letters of interest seem to expected post-interview here.