Are most Creoles a mix of African and French?

No.  "Creole" is more of a language term, but there are all sorts of peoples who speak a Creole.  The French speaking Acadians were moved from Canada, and mostly ended up in Louisiana, where many speak Creole.  Originally, they weren't African at all.

I don't know about most.  Some are based on Portuguese.

If you’re referring to Louisiana Creoles, then yes

Creole's are ethnic groups which originated during the colonial-era from racial mixing between Europeans and non-European peoples. These groups are typically descended from White Western European colonial settlers, West African slaves, Haitians and indigenous peoples of the Americas , Africa, and Asia.

I read a book on Spanish colonization once and remember that the first people labeled "Creoles" were the children born in the New World from 2 Spanish parents who were born in Spain.

The term mestizo means mixed in Spanish, and is generally used throughout Latin America to describe people of mixed ancestry with a white European and an indigenous background.

The term “mulatto” – mulato in Spanish – commonly refers to a mixed-race ancestry that includes white European and black African roots.Mestizos represent a racial majority in Mexico, most of Central America and the Andean countries of South America.Mulattos make up smaller shares of the populations in those countries – at most 4%, according to national censuses or other surveys. In Caribbean countries and Brazil, where populations with African ancestry are larger, mulattos make up a larger share of the population – 11% in the Dominican Republic and 47% in Brazil. (A 68% majority in the Dominican Republic identifies as “mestizo/indio.”)In Latin American colonial times, the Spanish caste system outlined all the different ways the native peoples in New Spain had mixed with Africans and Europeans – and the names and rights associated with each combination.