The font will show in calibre's ebook-viewer if your computer knows how to find the font.
But it won't show up on the Kindle unless the font is embedded in the book.
Conversions have the option to embed fonts, and add the extra CSS which makes the text
use said font at the same time.
The Editor has a Tool for embedding fonts too.
I don't know which one you used to add the CSS.
Now you already have the AZW3 without (?) embedded fonts, the easiest fix would be to go over it once more, with Polish book -- one of calibre's builtin tools.
See Preferences ==> Toolbar to add it to your toolbar or right-click menu.
Or use the shortcut key which defaults to "P".