Question when I hit play the mouse cursor automaticly gets set to 90 degree.

i have been trying different things and i cant for the life of me understand how this issue can be solved. also i am a beginner if it helps.
here is the code (yes i did a little bit of stealing)

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEditor;
4. using UnityEngine;
5.  
6. public class CameraScript : MonoBehaviour
7. {
8.     public float mouseSensitity = 50f;
9.     public Transform player;
10.     float xRotation = 0f;
11.     private void Start()
12.     {
13.         Cursor.lockState = CursorLockMode.Locked;
14.     }
15.     void Update()
16.     {
17.         float mouseX = Input.GetAxis("Mouse X")*mouseSensitity*Time.deltaTime;
18.         float mouseY = Input.GetAxis("Mouse Y")*mouseSensitity*Time.deltaTime;
19.  
20.         xRotation -= mouseY;
21.         xRotation = Mathf.Clamp(xRotation, -90f, 90f);
22.  
23.         transform.localRotation = Quaternion.Euler(xRotation,0f,0f);
24.         player.Rotate(Vector3.up*mouseX);                           //moves the entire body along the x axis
25.      
26.  
27.     }
28. }
29.