//Enqueue only if shortcode Exists on wp_content
add_action('wp_enqueue_scripts', 'myplugin_stylesheet');
function myplugin_stylesheet() {
global $post;
if( is_a( $post, 'WP_Post' ) && has_shortcode( $post->post_content, 'myplugin-shortcode-name') ) {
wp_enqueue_style( 'myplugin-style', plugins_url('myplugin-style.css', __FILE__));
}
}