It appears that the SSL configuration used is not compatible with Cloudflare. This could happen for a several reasons, including no shared cipher suites.
What is the issue you’re encountering
Inability to create a subdomain for my website.
Was the site working with SSL prior to adding it to Cloudflare?
The subdmain shown in your screenshot planningmywedding.renaymeshellevents.com doesn’t seem to exist any longer.
Have you removed the DNS record from Cloudflare?
As to the SSL error, this is usually caused by a bad SSL certificate at the origin server, and the easiest way to troubleshoot is is to set the subdomain to DNS-only and fix whatever issues you see at the origin.