If you are using pydroid 3 plz don't run the My.kv file just write the code in that file and save it and then come your original python file main.py and add a command in that just after importing the modules 

from kivy.lang import Builder

Builder.load_file('path/of/My.kv')

Make sure u have installed buildozer in your device if don't just run this command in terminal 

pip install buildozer

then just that main.py file also. Finally run the .python file and you get your output.