There's where all your space went... I'm not familiar with how to delete backups, but that's most likely what needs to be done.
Edit: Found it
Edit2: If your computer is as you would like it to be, I would personally recommend making an Image of the machine rather using backup. System backup is great, but as you can see, it quickly eats away at available space. Making an image will take a snapshot of the drive so that if things go south later on, you can restore it to the image. The only bad part about imaging rather than sys backups is the frequency at which sys backup makes file/settings copies whereas with an Image program you are required to make the image on your own and well, don't always have the foresight to know when things are about to go sour.
Humans are the only creatures that won't live up to the their potential. Give everything your all. When you die, die on E.
So I ask you, what do you intend to do now?