I would try a guess, since I didn’t actually get exactly what the issue is.
Your certificate is for something like sniXXXXX.Cloudflare.com, that is the normal Free certificate. It’s fine.
If your domain doesn’t open in HTTPS you usually just need to set Always Use HTTPS in the Crypto page in dashboard. The other option is the SSL setting, if your origin supports HTTPS you should set it to Full (Strict if the certificate on the origin is valid), otherwise set it to Flexible.