Backup doesn't finish yet still takes up space?

I'm trying to back up my iPad on my computer and back ups for me will only work on the local harddrive not an external. Now, it's been a long time since I've backed it up so it was taking a lot of time and space, but then it came up with the error that there isn't enough harddrive space for it to save so it just quits backing up.

But the thing that kills me is that I look on my capacity and it's been decreased incredibly (because it's still been saving some of my ipad's data) and since it never finished backing up fully I can't go into iTunes > Preferences > Backups and find it and delete the file because it's not there.

How can I find the data that it backed up on my Mac and how can I delete it? I'm so confused and now my Mac won't even work right because it literally has less than 10 mb of space.