How can I get Itunes on Mac to see all of my music?
iTunes uses an internal database for your song list. Move the songs you added manually from Finder to the Desktop (for example).

Check in iTunes settings that it's set to let iTunes manage the Music Library.

Open iTunes and drag and drop the song folder on iTunes (either the window or the icon in the Dock).

iTunes will then copy them and add them to its library.

You can now delete the songs you have on your Desktop.