I believe there might be a bug in the Domain Mapping plugin as it relates to Jetpack.
"Invalid request, please go back and try again.
Error Message: The URL stored by the Jetpack servers does not match your site. Please try disabling the Jetpack plugin, re-enable it, then connect again."
Could you try updating your Wordpress Cloud's data with your mapped domain (TLD domain not subdomain) ? And are you still getting this errors after deactivate and then reconnecting the jetpack ?