Problem in your SQL :
You can construct your sql like this :
$wpdb->prepare(
"INSERT INTO `wp_submitted_form`
(`name`,`email`,`phone`,`country`,`course`,`message`,`datesent`)
values ('$name', '$email', '$phone', '$country',
'$course', '$message', '$datesent')"
);
You can also use $wpdb->insert()
$wpdb->insert('table_name', input_array())