I am the queen of failed fudge, so I can give you lots of ideas. Or at least a couple!
First, it will make fabulous frosting. Just throw it in your freezer and, when you need some chocoalte frosting, thaw it out and whip some butter into it. This works even if you have nuts and such in it.
To rescut it as fudge, you can also do a couple of things. If you want it to be less sweet, find yourself some cocoa butter—the eating kind (try a health food store). Melt it, let it cool so it’s pretty cool but not solidifying, and mix it thoroughly into your room temperature fudge. It will probably take as much cocoa butter as you have fudge, so plan for a lot. It will still seem liquid after you do this, but, like chocolate, cocoa butter is solid at room temp, so as it comes to room temp (and you can throw it in the fridge) it will become a solid. You can also use chocolate the same way, which will contribute whatever sweeness the chocolate has.
To figure out how much cocoa butter (or chocolate) you need is this. Chocolate is solid. Your fudge is whatever it is. If you want it to be halfway between what it is and a total solid, use an equal weight of chocolate or cocoa butter.
If you don’t use enough, you can melt more and do it again!
When I do this, I also add “stuff” to it to sort of “break up” the mass—nuts, coconut, whatever.
No one will know it’s been rescued, unless you have people who really know their fudge stuff. I did this last Christmas, and the fudge was a real hit. Most people really liked it, too, becuase I used cocoa butter and the fudge wasn’t so teeth-rottingly sweet.