Srry for being late, i dont usually come to this site xd, The moment you travel to the center and meet Becca and Jinx For the first time i kind of remember, i think its the first encounter through the map, not the one when you first leave school, that encounter ends and a few days later or that same day if you open your phone it automatically starts the next part of becca's route, make sure to not open the phone so you dont trigger the next part, you can open it during night times so you can check the stuff you need without losing the chance to make the money, while you ignore your phone you can actually go to becca and work with her, this way you get the money to buy asuka's dress but you dont lose the chance to make all routes, once you get the money you need, you can open your phone and if you instantly get a message from becca then you did right.
If by any chance you still cannot make it, try to tag or pin mi on the game's discord server, i can manage to make a call or send at the server a video so you can follow the steps, dont you worry, im happy to help