When I log in with https I get a certificate mismatch warning. Is it okay to ignore this and log in ?
It is likely that your web host is using a self-signed certificate, or a signed certificate that does not match your domain name. This warning exists to notify you that the name on the certificate does not match the name of the domain you are trying to reach.
This should not be a security issue when logging into your site's cPanel interface. Check to make sure that the SSL certificate is from a domain that belongs to your host before proceeding. If you are concerned about security, contact your host to make sure it is safe to proceed.