Thanks for sharing. There are 2 small adjustments you need to make:
The box that sometimes shows up around your car is the last box added to the targets. It happens sometimes that when you add the car, the box has not been moved to its own position in time. To solve this issue, the best solution is to move the code for the targets and the car into 2 new sprites, as suggested in the tutorial steps 7 and 11 above
The plane can not be too big. The size given in the tutorial has y of 15000, and your project has 150000, which is 10 times larger. Although this seems to be a small difference, the physics engine can not find a solution when you try to drive the car. So try 15000 or some other smaller value. If you do need to have a larger map, you can add more planes, but keep each of them relatively small.