What makes this more ironic is she proclaims this on page 9 of all pages... Then again, Reimu did fall head over heals for this Cirno, so we shall see.
I suspect she knows she has a long way to go but puts on a show much like Remilia. Cirno's always depicted as much less intelligent than she really is. Even according to the original ZUN profiles, she was originally called childish, not stupid, though the 2 words are either written or pronounced the same. Can't remember which the Touhou Q&A About Everything said it was.
But..."So there are people like that too."I thought to myself...So I decided that...Ahaha...I'm pretty weak, though!I can't beat even one of her spellcards!...I see.I guess I felt regretful after that..."I'll definitely beat her, someday."