trouble with embedding the user register form in another page

I am trying to create a workflow for my role subscription module that includes registering in the same work flow so I call drupal_get_form('user_register') and embed the register form in my page. It kind of works, meaning if you register a new username it will work if you try to register an existing username it doesn't behave like the normal register page which will say "that username is already taken" - instead it tries to create the duplicate user again and fails and gives me a duplicate key error - why in the world is it doing that? Is there a better way to do this?