Might be talking through a hole in my head (colloquially speaking of course), but in the good old days you were able to get a roll "pushed", where you shot it at a lower ASA and had the processing compensate. I am not sure if "pull-processing" is/was available, but it was the first thing I thought of. It would of course require a specialist lab, and this will cost, but only you can tell if this is an option at all.
If not, then fire it through a simple cheap lab as negs only, and see, the cost will be minimal, and you just never know.
And before you feel too bad, I'll wager virtually everyone here has done the same thing, those that haven't either will, or have their heads buried in the digital age.
Gary