Hi there! It is completely normal to not be able to select the drink on the last visit; the final drink is automatically chosen for you based on the previous selections you made in the game. The game logic was designed this way, so please don't blame yourself!!
I'm going to post some hints below (if you want to read them) and hopefully you get to the other endings soon!
- Hint 1: the choices/selections you make when it's "gym" time have no bearing on the end result; they're there to give you a testing ground to see how the characters react to you; you can easily skip through these.
- Hint 2: You have to go all-in and choose the same type of drink every time you visit the club, in order to get a character-specific ending, and build rapport with that character exclusively: Fung tends to like to talk about himself, Sunny tends to like to talk about tea, and Ceilic tends to like to talk about what he's thinking. Of course compliments are generally liked by all! You can generally tell based on their reactions, what they like and what they don't like.
- Hint 3: You need to inception the guy to think/talk about the other guy (if you're hoping for those kinds of endings).
That's all for now :) Happy to reveal more if you are still having difficulties! Thanks for bringing all of this to my attention!