Yes! If you copied the HTML code from the setup page correctly then it is HTTPS (SSL) secured. The reason your website does not show this is because the surrounding website (your website) is probably not HTTPS secured, so the browsers have to show it as insecure. If you would link directly to the BookNow window it would show as secure.
If you want the show the padlock icon for BookNow when embedded in your website then you need to get a SSL certificate for your own website.