Problem with Look at mouse in a spherical world

Hi!

I'm creating a game where the world is a big sphere and where the player can rotate around(like super mario galaxy) but, for the orientation of the player, I want to use the mouse, so I take a "Look at the mouse" script, but when the player arrive at something like half the world/sphere he start to stop following the mouse, turn where he want, when he want.

here's my code:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerLookAt : MonoBehaviour {
 
         
         void Update () 
         {
             Plane playerPlane = new Plane(Vector3.up, transform.position);
             Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
             float hitdist = 0.0f;
             if (playerPlane.Raycast (ray, out hitdist)) 
             {
                 Vector3 targetPoint = ray.GetPoint(hitdist);
                 Quaternion targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
             transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, GetComponent<PlayerManager>().RotateSpeed * Time.deltaTime);
             }
         }
     }

can you help me please.