Character rotating in local space instead of world space?

Hey all, I'm currently creating a first person controller which will be used on a ring world (like this), but i've got a problem.

When I'm keeping the camera looking out of the ring world, the character moves fine, but once I look towards it, he starts rotating sideways. I believe it's because of the script rotating the player along the Z-axis in local space instead of world space, but i'm not really sure.

Here's my first person movement controller:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerMovement : MonoBehaviour
 {
     public float speed = 6;
     public Rigidbody rb;
     public GameObject center;
 
     void FixedUpdate()
     {
         //Rotate player towards center pivot
         Vector3 relativePos = center.transform.position - transform.position;
         Quaternion rotation = Quaternion.LookRotation(center.transform.forward, relativePos);
         transform.rotation = Quaternion.Euler(transform.rotation.eulerAngles.x, transform.rotation.eulerAngles.y, rotation.eulerAngles.z);
 
         //Debug stuff
         Debug.DrawRay(transform.position, relativePos, Color.green);
 
         //Move player based on current rotation of player
         Vector3 fwrd = Input.GetAxis("Vertical") * transform.forward * Time.deltaTime * speed;
         Vector3 rght = Input.GetAxis("Horizontal") * transform.right * Time.deltaTime * speed;
         rb.GetComponent<Rigidbody>().velocity = fwrd + rght;
     }
 }

Here's my camera movement script, if it's necessary:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerController : MonoBehaviour
 {
     public float mouseSensitivity = 100f;
     public float xRotation = 0f;
     public float speed = 5;
 
     public Transform playerBody;
 
     // Start is called before the first frame update
     void Start()
     {
         Cursor.lockState = CursorLockMode.Locked;
     }
 
     // Update is called once per frame
     void Update()
     {
         float mouseX = Input.GetAxis("Mouse X") * mouseSensitivity * Time.deltaTime;
         float mouseY = Input.GetAxis("Mouse Y") * mouseSensitivity * Time.deltaTime;
 
         xRotation -= mouseY;
         xRotation = Mathf.Clamp(xRotation, -90f, 90f);
 
         transform.localRotation = Quaternion.Euler(xRotation, 0f, 0f);
 
         playerBody.Rotate(Vector3.up * mouseX);
     }
 }

Here's a video. Where's the problem?