I am having the same issue. The funny thing is I have never added the site to any other place. I am just trying to map the netlify name as a URL to my domain on Cloudflare and I get the Not Found - Request ID: 01GC1VA4SF079NWGYH7WBF92V3 error. Not sure how to proceed.
Have you read through the documentation for configuring an external domain
and also read this support guide about using Cloudflare in front of Netlify?
If you are still having issues, can you please share the name of your Netlify site, and the domain you are wanting to attach to it.