Already booked the appointment for your wedding dress alteration in advance? (before the dress is coming)

I recently reached out to several seamstresses in Hamilton, ON for my wedding dress alterations, as my big day is coming up in August. My bridal boutique highly recommended booking in advance due to the peak season, but unfortunately, none of the seamstresses I contacted (I called at least 7 of them...) were able to secure an appointment. Am I missing something...?