Error upgrading OS on mid-2011 iMac

It's been a while since this happened... The update app on my iMac asked me to update my Mid-2011 iMac to Mojave. I went ahead and went through the installation process. I'm getting this error during the installation process: "macOS could not be installed on your computer An error occurred while loading the installer resources. Quit the installer to restart your computer and try again." I click the "Restart" button and it eventually hits the same error. I'm not able to get past it except rebooting in safe mode.

Silly me, in researching this I found that Mojave can only be installed on Late 2012 or later. I would have thought the update app wouldn't have given me the option to install Mojave if it wasn't compatible.

Is there a way to back out this upgrade?

Thanks,

Rich