Player moves slightly to the side?

Hey guys,

I have a small issue with my player movement. The movement in the script is based on the player's rigidbody.

 public void Walking()
     {
         if(Input.GetKey(KeyCode.UpArrow) || Input.GetKey(KeyCode.W))
         {
             rigidbody.AddForce(0,0,walkingSpeed);
             //rigidbody.velocity = new Vector3(0, 0, speed * Time.deltaTime);
             //transform.rotation = Quaternion.LookRotation(Vector3.forward);
             //rigidbody.rotation = Quaternion.Euler(0, 0, 0);
             //rigidbody.velocity = transform.forward * speed * Time.deltaTime;
         }
         
         if (Input.GetKey(KeyCode.DownArrow)|| Input.GetKey(KeyCode.S))
         {
             rigidbody.AddForce(0,0,-walkingSpeed);
             //rigidbody.velocity = new Vector3(0, 0, -speed * Time.deltaTime);
             //transform.rotation = Quaternion.LookRotation(Vector3.back);
             //rigidbody.rotation = Quaternion.Euler(0, 180, 0);
             //rigidbody.velocity = -transform.forward * speed * Time.deltaTime;
         }
         if (Input.GetKey(KeyCode.RightArrow)|| Input.GetKey(KeyCode.D))
         {
             rigidbody.AddForce(walkingSpeed,0,0);
             //rigidbody.velocity = new Vector3(speed * Time.deltaTime, 0, 0);
             //transform.rotation = Quaternion.LookRotation(Vector3.right);
             //rigidbody.rotation = Quaternion.Euler(0, 90, 0);
             //rotate += rotateSpeed*Time.deltaTime;
         }
         if (Input.GetKey(KeyCode.LeftArrow)|| Input.GetKey(KeyCode.A))
         {
             rigidbody.AddForce(-walkingSpeed,0,0);
             //rigidbody.velocity = new Vector3(-speed * Time.deltaTime, 0, 0);
             //transform.rotation = Quaternion.LookRotation(Vector3.left);
             //rigidbody.rotation = Quaternion.Euler(0, -90, 0);
             //rotate -= rotateSpeed*Time.deltaTime;
         }
 }

You can take a look at the problem here.

I tried a couple of different things, but no success. I noticed that the player's collider box slightly sinks into the floor. Might that be the problem since he has a rigidbody and maybe the collision with the floor brings the object off from course?