I am not sure, what you created - a shared album or a slideshow project?
You can use a shared album to share videos and photos, but not a project, see:
Use Shared Albums in Photos - Apple Support
To share a slideshow as you created it in your slideshow project (including the titles and the background music) export the finished slideshow as a video. Open the slideshow project and click the Export button in the toolbar. Then select a video quality and save the video. I would share this video by mail drop. If you import it back to Photos to add it to a shared album, the size and quality will be reduced.
Or share the photos from your album as a shared album. (What are shared albums in Photos on Mac? - Apple Support)
Add the photos to the shared album exactly in the order you arranged them, one by one. If the photo needs an explanation, add a comment. People you invite will be seeing your comment as a title below the photo on the webpage, when they are viewing the album on the web. They can view the photos individually by stepping them or play the sequence of photos as a slideshow.