How to rotate/move diagnal with rigidbody sphere

Having trouble with the physics here. I want the player(sphere game object) to be able to roll in every direction to navigate through the platform course. I can now go back and forth but trying to go to the side or diagnal isnt working properly here is the script. What am I doing wrong exactly?

  UnityEngine;
 using System.Collections;
 
 public class SphereController : MonoBehaviour {
 
 
     //The constant forward speed.
     public float sphereSpeed;
     //The user controlled left and right speed.
     public float leftRightSpeed;
 
     //Win or Loss.
     public bool win;
     public bool gameOver;
 
     //The visual partical effect for when we collide.
     //Just a cheap example.
     public GameObject prefabVisual;
     
     
     void Update () 
     {
         rigidbody.AddForce(Input.GetAxis("Horizontal"), 0, 0 * leftRightSpeed);
         //transform.Rotate(new Vector3(0,Input.GetAxis("Horizontal"),0));
         rigidbody.AddForce(0, 0, Input.GetAxis("Vertical") * sphereSpeed);
         //Move forwards or backwards.
         
 
         if (transform.position.z >= 19)
         {
             win = true;
             //Disable movement of the sphere.
             //Here we could load a different scene. Win screen, highscore screen, etc.
             this.gameObject.GetComponent<SphereController>().enabled = false;
         }
     }
 
     void OnCollisionEnter(Collision other)
     {
         //If we hit a obstacle.
         if (other.gameObject.tag == ("Obstacle"))
         {
             //Tell us what we hit.
             Debug.Log("Hit an obstical" + other.gameObject);
             
             //gameOver = true;
 
             //Instantiate the prefabVisual.
             Instantiate(prefabVisual,transform.position,transform.rotation);
             
             //Disable movement of the sphere.
             this.gameObject.GetComponent<SphereController>().enabled = false;
             
             //Make the sphere dissapear.
             this.gameObject.GetComponent<MeshRenderer>().enabled = false;
             //Could add a game over scene now.
         }
     }
 }