Script offset problem \(>.<)/

I'm making a 2d platformer where a player is controlled by the arrow keys , so far he can go left and right. I'm using a sprite sheet that I created resolution is 5337x796 its a simple walk-cycle 1 row and 8 columns. I'm using a plane to control the image.

THE PROBLEM:
the problem is that when the character moves the offset changes on the y axis, but since my image is 1 row ,well it looks weird. how can I alter my script to change the offset on the x axis instead of the y(like its doing currently).

Script:

 using UnityEngine;
 using System;
 using System.Collections;
  
 public class Test : MonoBehaviour
 {
     public int columns = 2;
     public int rows = 2;
     public float framesPerSecond = 10f;
         
     
     
     public float TranslationSpeed = 0.5f;
     public float RotationSpeed = 500f;
     float animationTime = 0f;
     int lastDirection = 1;
     
     //the current frame to display
     private float index = 0;
  
     
     
     void Update ()
     {
         // Get a value that indicates if the right/left keys are pressed:
         float horiz = Input.GetAxis("Horizontal");
         
         #region Translation
         // Move the character based on the right/left key press:
         float motion = horiz * Time.deltaTime * TranslationSpeed;
         transform.Translate(motion, 0, 0, Space.World);
         #endregion
         
         
         #region Cartoon animation
         animationTime += Math.Abs(horiz) * Time.deltaTime * framesPerSecond;
         if (animationTime >= 1f)
         {
             animationTime--;
             index++; 
             
             if (index >= rows * columns)
                 index = 0;
             
         }
         
         #endregion
         
         #region Flip figure
         // Figure out which direction the model should face based on the movement direction:
         int faceDirection = Math.Sign(horiz);
         if (faceDirection == 0) // If the model isn't moving, then keep it facing the previous way.
             faceDirection = lastDirection;
         lastDirection = faceDirection;
 
         // To give the impression of a piece of paper being flipped over, rotate the model to face the new direction over a period of time:
         float angle = transform.localEulerAngles.y;
         if (faceDirection == 1 && angle < 180f)
         {
             angle += Time.deltaTime * RotationSpeed;
             if (angle > 180f)
                 angle = 180f;
         }
         else if (faceDirection == -1 && angle > 0f)
         {
             angle -= Time.deltaTime * RotationSpeed;
             if (angle < 0f)
                 angle = 0f;
         }
         transform.localEulerAngles = new Vector3(0, angle, 0);
         #endregion
         
         
     }
         
         
         
     void Start()
     {
         StartCoroutine(updateTiling());
  
         //set the tile size of the texture (in UV units), based on the rows and columns
         Vector2 size = new Vector2(1f / columns, 1f / rows);
         renderer.sharedMaterial.SetTextureScale("_MainTex", size);        
     }
  
     private IEnumerator updateTiling()
     {
         while (true)
         {
           /*  
              //move to the next index
             index++;
             if (index >= rows * columns)
                 index = 0;
              */
         
  
             //split into x and y indexes
             Vector2 offset = new Vector2((float)index / columns - (index / columns), //x index
                                           (index / columns) / (float)rows);          //y index
  
             renderer.sharedMaterial.SetTextureOffset("_MainTex", offset);
  
             yield return new WaitForSeconds(1f / framesPerSecond);
         }
  
     }
 }