My enemy cube moves through walls

Hi, I am a beginner at using unity and after doing the roll-a-ball tutorial I decided I am making a platformer project using the movement concept from the tutorial. I have gotten to the point where I want to add obstacles and "enemies" that need to be avoided. Right now I am basically trying to get the enemy to pingpong between x values so that it moves back and forth and therefore makes the player have to avoid it to progress.

Well, right now I am using this code for my script.

     public float speed = 3;
     public float startingX;
     public float targetX;
     public float direction;
 
     void Update () {
         transform.position = new Vector3(direction * Mathf.PingPong(Time.time * speed, targetX * 2) + startingX * direction, transform.position.y, transform.position.z);
     }
 }

And the problem is the enemy is not ping ponging and ends up moving through the wall boundaries and going on in the x positive direction to infinity and beyond. Can anyone help me? It'd be much appreciated. As well as any explanations to help me understand what is happening would be lovely.