Notes not syncing with Mac

I'm trying to set up Notes to sync across my Mac and iPad (I checked, and it is not currently working).

On the iPad, I went to Settings. Mail, Contacts and Calendars and enabled the on/off switch next to Notes, but i got the message that to turn on notes i must create a free iCloud account, with a "Cancel" or "Create" option.

I recall that I had already set up an iCloud account, but there was no button with the option "I have already set up an iCloud account."

What do I do next?