"When did this become a self-insert game...?"
This line is made of win. 
Poor MC, the last thing she wants to be is a Mary Sue... yet the heroine just said "Suki!" to her, and she's been inadvertently winning the heart of the villainess, and now she has accidentally started the romantic route with the prince.
Has she isekai-ed into the universe of the game, or the universe of a Mary Sue's fanfiction of self-satisfaction? It's a perfectly valid question. 