I just installed Garageband on my mac but I don't know if it charged my card
There is an easy way to check this. Go into iTunes and click the Store tab. Once it has loaded, scroll to the very bottom of the page, and under Manage you will see a link to your Account. Click there and sign into your Apple ID if prompted, then under Purchase History click See All. This will give you a list of all the apps you have downloaded from the App Store, iTunes store, and other Apple services. Find GarageBand in the list, and if the price is labeled as $0.00, you will not be charged for the app. But if it is labeled otherwise, you will be charged for the app.