That backup size is probably the whole C drive, OS, apps and data included.
You can delete D drive and then expand C drive to use the extra space. Then set up windows System Restore to create snap shots of the C drive.
Maybe get an external HDD and clone windows to it.
And to create a windows recover disk in windows 7:
1
Click the Windows “Start” button and select “Control Panel” from the menu. Click “System and Security,” then select “Backup and Restore.”
2
Click "Create a System Repair Disc." If you have more than one optical drive installed on your PC, choose your preferred CD/DVD burner from the drop-down menu. Place a blank CD or DVD in the drive tray and click "Create disc." A progress bar...