May I ask you to share more relevant feedback information with us here?
What is your domain name?
Have you individually added your domain name to your Cloudflare account and changed domain nameservers at your domain registrar?
Before moving to Cloudflare, was your Website working successfully over HTTPS?
What kind of error do you experience?
Can you share a screenshot of it here with us so we could troubleshoot and double-check?
Regarding the management of the DNS records at Cloudflare dashboard, below articles & tutorials could help you with that as far as they containt step-by-step instructions: