Make sure your sync is active - Admin -> SFDC -> check the timestamp in the top right.
Check for errors in the notifications tab in My Marketo.
Check that the campaign member statuses in SFDC match the program member/channel statuses in Marketo
Take a campaign member from SFDC and search for there email address in Marketo Lead database and see if they exist (if not it could be a permissions/visibility problem in SFDC).
Reach out to support if the above doesn't help the issue.
Run a smart list on Member of SFDC Campaign to see if Marketo knows they are members already.
You may have to try manually updating their Program Member Status, although you should not have to.
How long have you been waiting for the sync? For some reason, it took a bit of time yesterday for my campaign members to sync over, but they eventually did. Of course, if it's more than an hour or so, I'd log a case with support.
Yes it finally got Synced but for some reason it took more time than usual