if(sanitize_text_field( $_POST['com_submit']) != '' {

        if ($_REQUEST['bg'] != "681")  {

            $error_msg = __('Грешен отговор на въпроса.','');

        }

        else {

        $firstname=sanitize_text_field( $_REQUEST['com_firstname'] );
        $lastname=sanitize_text_field( $_REQUEST['com_lastname']);
        $username = sanitize_text_field(  $_REQUEST['com_username'] );
        $email = sanitize_text_field(  $_REQUEST['com_email']  );
        $bg = sanitize_text_field(  $_REQUEST['bg']  );
        $password = $wpdb->escape( sanitize_text_field( $_REQUEST['com_password']));
        $status = wp_create_user($username,$password,$email);
        $succress ='';
        $error_msg='';


        }

The rest of your code here ...