My picture is almost completely black

My picture is almost completely black

I had a picture taken that is really important to me, it printed nicely, but I noticed that it didn't develop properly. I brought it home and just set it down in hopes that it would develop further, but it hasn't. I would really like to have the picture, but you can hardly even see it because it's so dark. Does anyone know how to fix this, or is it beyond repair now that the picture has been taken and its a few days later?