In a livestream, Marco does acknowledge that Janna is flirting with him (I don't have the book, I said multiple times that I work on the Tv Tropes page for SVTFOE and there is a tag dedicated to the ship tease moments in the series).

Personally, I like the idea of this ship and I wouldn't be against it if it was acknowledged in the series or even added but I think Janna is play flirting with him, I've met plenty of people who are like Janna.

I ship it too—

now I have like four ships that include Marco—

It's a harem.

Which page of Star and Marco's Guide to Mastering Every Dimension has this "not ready to date someone as fierce as me" line?

Noticed trivia says:

"The book is credited to have been written by Star Butterfly, Marco Diaz, and Pony Head "with help from" Dominic Bisignano, Amber Benson, Devin Taylor and Cindy Plourde."

Do not see Janna credited. Is it possible that Star actually wrote this and wanted Marco to think it was Janna so he would not pursue her? Or that Marco wrote it as a joke?

IRL: assuming Nefcy has last say on every episode script, did she have a last say in what was included in this book? Wondering where it falls in canonicity hierarchy.

Ah so, do we know who did the interview and if they are a competent transcriber of answers? Maybe Star has horrible shorthand or she tried to jot it from memory, but her imagination merged with the memory and altered it.