I'll dispatch with the semantics first so others who may happen upon this are not confused. You did not fill out a K1 visa application, (the beneficiary does that), what you would've completed was a I-129F petition form.
Your record may have been expunged, if that's the case, then you can't be legally penalized for non-diclousure as you are allowed to treat something that's been expunged as if it's never occurred. In addition, you're already past the point of disclosure on your end.
With that being said, does your fiancee know about it? You may want to tell her about it just in case she specfically gets asked about it during the visa interview.
Disclaimer: I'm not a lawyer and what I've said abouve should not be taken as legal advice, it's only general observations of what I've observed over time.