Why is my Mac display wrong storage space? HELP!

First of all, the picture shows up your MacBook Air's serial number, so I have asked the hosts to edit your question.

Sometimes your Mac may show up a wrong storage space due to Spotlight, so in order to fix the issue you have to reindex the OS X drive. To do it, follow these steps -> Spotlight: How to re-index folders or volumes - Apple Support (in your case, you have to add the partition labelled as "Mac" to the list).

Try re-indexing Spotlight: Spotlight- How to re-index folders or volumes - Apple Support. Wait until it finishes which can take a while, then check the display but not before indexing is complete.