If you flashed the factory image you're stock and not rooted, right? But yes you shouldn't lock the bootloader again after modifications. You can relock it after flashing factory image from google though if you fon't flash anything else and don't modify it. That's also the only way to get google pay to work without root and Magisk hide.
Also, as long as you don't untick "enable oem unlocking" in developper settings, you can still unlock if it bricks, as long as you have fastboot access. So if you happened to brick by relocking, just unlocking again (and flashing if needed) would solve it anyway.