moving obstacle overshooting

obstacle moves between 2 declarable points but it keeps overshooting the points when i run it

using UnityEngine;

public class MovingObstacle : MonoBehaviour {

 public Rigidbody rb;

 public float xForce = 100f;
 private double startPos;
 public float offset = 10f;
 bool leftMove = false;
 bool rightMove = false;

 // Start is called before the first frame update
 void Start()
 {
     startPos = rb.position.x;
     rightMove = true;
 }

 // Update is called once per frame
 void Update()
 {
     if (rb.position.x >= (startPos + offset))
     {
         rightMove = false;
         leftMove = true;
     }

     else if (rb.position.x <= (startPos - offset))
     {
         leftMove = false;
         rightMove = true;
     }
 }

 void FixedUpdate()
 {
     if (rightMove == true)
     {
         rb.AddForce(xForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);
     }

     else if (leftMove == true)
     {
         rb.AddForce(-xForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);
     }
 }

}