Do I own the IP of software I built in my spare time as a non-developer, if I’ve now used working hours to develop it?

I’m an analyst for a restaurant group. I built an app while I was furloughed, which the company I work for now uses & I’ve used working hours to continue to develop it. The CEO has said he wants to sell it to other companies. Do I own the IP? My contract doesn’t mention I build software or have any IP provisions.