GPX Downloader is an extension for Google Chrome that will let you easily download the course you created on Garmin Connect.

You will need to make sure that you have the latest version of the browser and the extension, as well as the most recent version of the Garmin Connect app. If you are using a tablet or iPhone, you will also need to make sure that you have the latest version of the app installed.

Once you are on the site, you will see a download button that will allow you to download the course in the GPX format.