cant add script

  using UnityEngine;
  using System.Collections;
  
  public class GotoMouse : MonoBehaviour {
  
      public float speed = 1.5f;
      private Vector3 target;
  
      void Start () {
          target = transform.position;
      }
      
      void Update () {
          if (Input.GetMouseButtonDown(0)) {
              target = Camera.main.ScreenToWorldPoint(Input.mousePosition);
              target.z = transform.position.z;
          }
          transform.position = Vector3.MoveTowards(transform.position, target, speed * Time.deltaTime);
      }    
  }

i am trying to add this script to my 2d object the object has a 2d box collider and an 2d rigidbody please help me!