Well u dont know phpBB and have not used it

To get into admin panel you have to login twice
this is for extra security and sall phpB bords have this feature
and there is no need of posts to keep the account active

you dint do anything wrong
you got the board wothout posting its not a problem
the forum is made for the support and to make good use of the services
Not to trouble you by making you post to keep account alive