Are you the original owner of the bike? Cannondale may be able to replace the frame.

The middle of the top tube should be stronger than the joints. But, I would worry if there is hidden damage in the frame much larger than the spot you're seeing. Any other places on the frame with those "worm tracks"?

You're in Indiana, so I'd imagine you get limited ocean exposure... but do you also ride that bike in the winter?

As others have mentioned, I'd probably ride it, but also start paying very close attention to it. And, start looking for a new frame to build up with my old components. Or, maybe keep that one as your winter bike, and start hunting for your +1 summer bike.