The quoting and insisting 다고 pronounced with a 구, which sounds softer and more coaxing: I said I do not want to; I believe in RM; I really want to get this one right. One line adds 요 for the polite 다구요. The grammar is identical to 다고, and the spelling simply signals a chattier, more affectionate delivery.
Register: casual and affectionate; nonstandard spelling