Incredibly frustrated with the android zwift app and companion. Dont even know if im in the right topic. Wanted to join a race in A but joined in D instead by accident. Upon realization y tried to quit and rejoin. Tapped the category several times in the android app to choose the right category and when im finally in the game changes me to C cat…ahhrrg! 
in summary missed the race trying to get to the right category! Soo mad 
Zwift don’t assign categories (I wish they would).
Using the companion app to sign up is a lot easier. You can also check your category beforehand.