Image distortion

[mcobb]

Here is portion of the image I'm working on    http://postimg.org/image/we8uxtffz/

I made this mosaic looking effect with a simple white background between the tiles. I decided to try using the soft eraser to make a gradient effect on some of the tiles but I ended up not liking it so I simply closed the program and told it not to save so I could go back to before I tried the gradient. When I opened the file again it looked like this. You can see where I tested the eraser near the bottom and then all of the tiles have this hazy gray outline. I erased around some of them in the top left, that's what it was supposed to look like. This isnt the first time something like this has happened. Can I fix it? What's going wrong in the first place?