Try a different method of stopping sign_ups

app/controllers/registrations_controller.rb

@@ -1,10 +1,10 @@
 class RegistrationsController < Devise::RegistrationsController
 
-  before_action :one_user_registered?, only: [:new, :create]
+  before_action :one_user_registered, only: [:new, :create]
 
   protected
 
-  def one_user_registered?
+  def one_user_registered
     if User.count == 1
       if user_signed_in?
         redirect_to root_path

app/views/layouts/application.html.erb

@@ -16,6 +16,7 @@
       <li><%= link_to "Edit account", edit_user_registration_path %></li>
       <li><%= button_to "Log out", destroy_user_session_path, method: :delete %></li><% end %>
     </menu>
+    <br/>
   </div>