I did that once to myself: Instead of selecting 16GB flash disk as target for the image, I have selected an external hard drive.
Being lazy (hopefully, I had nothing important on that hard drive), I used
TestDisk and I was able to recover majority of the files there. Directory structure was mostly lost, but this did not matter.
To the OP: If you can afford, borrow / buy a hard drive big enough to make first an
image copy of the corrupted disk. That copy would (and will) take ages to execute, but you will have peace of mind that you can try as many recovery tools as you like.
The way I recovered my hard drive: I ran TestDisk under Linux, and it operated on a file image of corrupted disk.