When you're at the choice of going left, right, middle, or taking flight, choose middle, which should take you to Chen. Choose to follow her and then choose to leave at the next choice, and you should find Flandre.
Erm, the 'Help Cirno/Don't help Cirno' choice is broken. According to the scans, 'Don't help Cirno' should lead you to Rumia eating you, but it instead brings you to Cirno's banter.
Ah, also, 'Middle' and 'Right' are mixmatched in the sign choice. Middle should take you to Alice and Right should take you to the Yakumos, according to the original scans.