Assigning new userse

I bought a 3 seat starter plan and after setting up my primary account I am not able to add the 2nd and 3rd user.  Under the Users and Groups page of the Admin Console it says 3 of 3 seats used but I only setup 1 managed user.  When testing I also have external users setup, does this also count as a user seat?  If not, how can I add additional managed users?