What I have noticed is that to exit the shop you have to click on "farewell" option while talking to Mandy. Which is the second option and is pretty easy to miss while tapping the screen to skip the text. Also the text options in the chat being pretty small are easy to misclick, which in this case would lead you again back into the shop menu.
I am working on improving these inconsistentcy or bad design choices in the upcoming demo and 0.11.0 build. So there will be changes for a better and uniform conversation behaviour in general with focus on things like: text scroll sound for all the ingame conversations, a better more spacedout choice display, etc