Unfortunately, you can't just ignore grammar to make something look nice. There are very few examples of paenitet used personally (L+S dictionary cites two from Livy, one of which could be interpreted as still impersonal, one from Sallust, who goes out of his way to do everything weirdly, and two instances of paenitens in Suetonius. The rest are not classical Latin examples).
On a slightly related note, the original English sentence sounds very good with the repetition of —thing. That repetition would not be preserved in Latin. Therefore I think that no matter what translation we come up with, the English will still sound better.
