date.php shows only three posts’ title. how to fix it?

Use the pre_get_posts action to modify number of posts per page on date archives. This would go in your theme’s functions.php file:

function wpa_date_posts_per_page( $query ) {
    if ( !is_admin()
        && $query->is_date()
        && $query->is_main_query() ) {
            $query->set( 'posts_per_page', -1 );
    }
}
add_action( 'pre_get_posts', 'wpa_date_posts_per_page' );