I'm on scene 115 and I keep getting messages about opening the cafe on chapter 3 scene 4 - how do ..

Once you've reached chapter 3 scene 4, you should receive an icon of a green armchair, bottom right. Tapping this will take you to the lounge. Tap on the tea set icon at the bottom to enter the cafe, where you can share drinks with other players on your boat friend list. Because you are past chapter 4 scene 2, you can also join or start a club and play in competition.