I've underexposed some negs by roughly this same amount: thought it was 400 bulk loaded in a container marked 100 but it actually was Delta 100. Went for a late afternoon stroll, shot some in the relative near dark my city gets to and even with 1/30th and f/1.4 I needed an effective rating of 1600.
I put it in some HC110 1:100 and let it stew for 2 hours with agitations every 15 mins. The negs aren't anywhere near perfect but they gave me images that I wouldn't otherwise have so I'm glad I didn't just throw the roll away. Plus, now I know what that looks like.
Mistakes happen, it's part of the process. Why not try it???
I put it in some HC110 1:100 and let it stew for 2 hours with agitations every 15 mins. The negs aren't anywhere near perfect but they gave me images that I wouldn't otherwise have so I'm glad I didn't just throw the roll away. Plus, now I know what that looks like.
Mistakes happen, it's part of the process. Why not try it???

It sounds like you might've read the poem "Candidate for a Pullet Surprise."