Main Site www.eatfully.com works
Added a new subdomain marmaris.eatfully.com to use a new root category but when i hit the website i see categories from default site and an OOOPS message
No errors on magento logs any help would be appreciated
I guess you created a new store associating a different root category, and you specified the "unsecure base URL" and the "secure base URL" for that store in the system configuration.
Have you updated the index.php and .htaccess for the multi-store setup?
Here is a very complete guide: https://www.cloudways.com/blog/create-and-configure-multistore-magento-2/