adding a table to db with dbDelta not working on activation

I am trying to add a table to the database upon activation of my plugin but it’s not adding it. also, it’s not storing the value of a global variable with add_option. please help!

here is my code

function atf_install() {
   global $wpdb;
   global $atf_db_version;
   add_option("atf_db_version", $atf_db_version);

   $table_name = $wpdb->prefix . "wptwitipid";
   if($wpdb->get_var("show tables like '$table_name'") != $table_name) {
      $sql = "CREATE TABLE " . $table_name . " (
      id mediumint(9) NOT NULL AUTO_INCREMENT,
      email varchar(120) NOT NULL,
      twitid varchar(120) NOT NULL,
      KEY email (email)
      );";
      require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
      dbDelta($sql);
   }
}
$atf_db_version = "1.0";
register_activation_hook(__FILE__, 'atf_install');