Apple is not very specific about the content of the in-app purchase. See:
Expanding GarageBand for Mac (v10.0) content with an in-app purchase
http://support.apple.com/kb/HT6031
With a one-time in-app purchase of $4.99 (USD), you can expand this content to 200 sounds, 2,000 loops, 15 drummers, and 40 basic lessons for guitar and piano. You also gain the ability to purchase additional Artist Lessons.
To see, if your in-app purchase installed correctly, ad a drummer Track to your project, and check, if you now have more than just the drummer SoCal. Also, you should able to purchase more piano and Guitar lessons for free from the Lesson Store in the opening panel, when you select "File > New"
You will only see the 2000 loops in the Loop Browser however, if you disable "keyword browsing" in the GarageBand Preferences "Loops" panel.
Have you checked of the saxophone instruments in the "Studio Instruments > Woodwind" section, if they would suffice for your needs?