You're still running the developer preview, a factory reset will not remove it. You will need to run the Nokia software recovery tool in order to restore windows phone 8.0.
You won't get windows phone 8.1 through settings-> update until Microsoft fixes the issue with bitlocker. Your alternative is to downgrade to Windows phone 8.0 using the Nokia software recovery tool, but only do this when you're sure that the update is available to download for your region/carrier/phone.