cannot get /admin for Activeadmin

I have an existing app with Rails 3.2.17 and angular js. I would like to include Activeadmin in the existing app.

I followed the steps from active-admin post from ryan bates. I performed following processes:

1. Added gem activeadmin in Gemfile
2. Run bundle install
3. rails g active_admin:install --skip-users (as I already have devise)

I have following routes if I run rake routes:

          admin_root             /admin(.:format)                                                           admin/dashboard#index
          admin_dashboard GET    /admin/dashboard

Then I restart my rails server and go to localhost:3000/admin. I have an error that says cannot get /admin. Can anyone please let me know if I am missing anything?