The MC should have refused the challenge from the start. The proper thing to say was: "You have become a real adult, you have a proper job, you are a productive member of society, while I'm still a worthless street delinquent who hasn't changed since her school years. It's my loss."
Btw, yelling in the opening chapters "I will never fall in love with you!!!" is like raising a huge endgame flag that reads: "And they married, had many children (even though they both are girls) and lived happily ever after!" Just sayin'. :P