[dnanian]

So, you stored your sparse image on your startup volume, which filled it? (Weird, because as I recall it explicitly disallows that.)

Anyway, delete the image file (which should be where you left it) and empty your trash. If that doesn't work, use Finder's "Go To Folder" command to go to the /Volumes folder. Make sure you've got any external drives ejected. Are there folders there with the name of the sparse image or any ejected volumes?