How to fix error getting data from MySQL COUNT?

I have joined two tables without problems, but in the last union I am having problems, specifically in the valuationsone that is numbering the value of products that do not have a value, for example:

The prueba 1, has no rating (that is, no user voted for this product) however the value is appearing (1)to me instead prueba 2if it has two users who have voted for that product.

So how can I fix this little error, this is my query:

    $stmt = $con->prepare("SELECT co.id_course,
                                    au.author,
                                    ca.program_lang,
                                    co.study_program,
                                    co.launch,
                                    co.start_date,
                                    co.release_date,
                                    co.title_course,
                                    co.subtitle_course,
                                    co.price_old,
                                    co.price,
                                    co.url,
                                    AVG(ra.rating) AS avg_rating,
                                    COUNT(*) valuations
                            FROM tbl_courses co
                            JOIN tbl_category ca ON co.category = ca.id_category
                            LEFT JOIN tbl_author au ON co.author = au.id_user
                            LEFT JOIN tbl_ratings ra ON co.id_course = ra.id_course
                            WHERE ca.program_lang = ? AND co.active = ?
                            GROUP BY co.id_course
                            ORDER BY co.id_course DESC
                            LIMIT ?");