How can I revert to my working iMac?

I used OCLP on my mini mac and everything worked fine but on my iMac I was getting stuck on "less than a minute remaining" I read it can take a long time, but I waited for days.

Now I just want to go back to my 10.13.6 and can't get it to work. The bar under the apple never finishes to load. I've created a bookable 10.13.6 USB but I'm not getting anywhere with this.

Is there a way to revert back to pre OCLP or is my only hope complete format and reinstall?