Hi all!
There is one thing that irks me about this lesson and that’s hardcoding the numbers, like 16 blocks, directly in the code. If we were to create a different level, this would have to be rewritten. Also, I did some stuff differently earlier and couldn’t follow this lesson 100%.
I found another way to move the block that should work in another situations as well and I thought I’d share 
It depends on ScreenToWorldPoint method of a Camera game object (here using the main camera) that does the conversion of position in pixels to position in world units.
Vector3 cursorPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
Vector3 screenBoundary = Camera.main.ScreenToWorldPoint(new Vector3(Screen.width, Screen.height, 0));
transform.position = new Vector3(
Mathf.Clamp(cursorPosition.x, -screenBoundary.x + transform.localScale.x / 2, screenBoundary.x - transform.localScale.x / 2),
transform.position.y,
transform.position.z
);