Exercise 4.2 Problem

Hello!
For exercise 4.2 i am not getting the required result as told (screenshot attached)

roslaunch blob_tracking move_ball_keyboard.launch
with this command ball moves but not the turtlebot3, some one can tell whats the problem in it?
Thanks

This usually happens if you have not been skipping certain parts of the course. Have you followed the course from the beginning without skipping any parts?