You waited a whole month? Some people waited years, I'm still "waiting" after 20 months! Be patient.
Ryr does not give a toss about your base choice in your application. At most it comes up in your interview.
And you can change it anyway, if you log into your account. If you cannot change it, then your application is already "under review". Does not mean they'll ever call you though, mine has been locked/under review for probably 7 months now.
@circle to land: Good point! Didn't think of that