First I'm not a Realtor but my company does own many rental and investment properties in Napa & Solano county. If your property is located in Napa county and not the city which I assume by the lot size mentioned that would be the case it sounds like you did the conversion into a 2 family without permits. Multifamily is not allowed in the county except in very limited cases, maybe yours is one of those exceptions albeit unlikely.
Three potential issues @Michael Cavalli.
1) If you rent the property and some calamity occurs, earthquake, fire, tenant accident, whatever and the tenant is hurt or killed on/in the property that was converted without permits you would be criminally liable.
2.) If the property has non permitted work it will be near impossible to secure a loan for a buyer to purchase the property. A simple review of tax records (1 click on the MLS) and it will show if your MLS entry (beds/bath/Sq ft) matches tax records. If not most seasoned agents will not even show the property.
3.) Price, in the real estate bull market we were in pre COVID-19 if you didn't receive an offer in the first 3-4 weeks price should have been adjusted down 3%-5% and repeated every 3-4 weeks until sold. If you go more than 90 days on the market without an offer it's price, a major issue with the property or both.
I record The Napa Valley Real Estate Report daily from my building at the Napa airport. We cover properties for sale in Napa Valley and Solano. Since I'm not a Realtor I break down properties in detail in a way no Realtor ever would. We have over 1,000 viewers from Napa Valley daily, check it out https://tinyurl.com/uftxleh