How can I save the content I created in my ArcGIS Online account before it is deleted at the end of the course?
If you are the owner of the content, you can export it to a variety of formats through the Item Details page.
Use layers—ArcGIS Online Help | Documentation
Hope this helps!
In addition, you can back up an organization's content in ArcGIS Online by exporting individual copies of the data to a local machine. Here is more info on the export process: