Why does my camera rotate on the x axis because of this script? What is wrong with the script?

This script should rotate the camera on the x axis.. The target is the tps player, but the camera rotates on the x axis whenI test my game and the rotation is too big so you dont see much more than the charater... Please help, I appreciate it.. Thanks!

using UnityEngine; using System.Collections;

public class CameraRotation : MonoBehaviour { [SerializeField] private Transform target;

 public float rotSpeed = 1.5f;

 public float _rotY;
 private Vector3 _offset;


 // Use this for initialization
 void Start () {
     _rotY = transform.eulerAngles.y;
     _offset = target.position - transform.position;
     
 }
 
 // Update is called once per frame
 void LateUpdate () {
     float horInput = Input.GetAxis("Horizontal");
     if (horInput != 0)
     {
         _rotY += horInput * rotSpeed;
     }
     else
     {
         _rotY += Input.GetAxis("Mouse X") * rotSpeed * 3;
     }

     Quaternion rotation = Quaternion.Euler(0, _rotY, 0);
     transform.position = target.position - (rotation * _offset);
     transform.LookAt(target);   
 }

}