I found out that some say that you have to step out of the shower after washing the head and the neck. Is that an obligation? No one taught me that, neither have I seen it in online videos about it. Is then my previous ghusls invalid? As in I have been to ziarah, prayed and fasted. Is all that void?

1- Yes, that is required based on the obligatory precaution
2- Nothing on your previous acts