How to limit rigidbody rotation to one axis at a time?

I am working on a plat-former where a cube moves by adding force to a rigidbody and it rolls. However, after a bit of constant rotation along the the Z axis(moving along the X axis) it will start to roll in the X direction as well and fall off course. How would I make it rotate only one direction at a time? Below is the code for the movement.

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour 
 {
     public float speed = 20;
     public float jump = 20;
     
     void Start () 
     {
         
     }
     
     void Update () 
     {
         if(Input.GetKey(KeyCode.RightArrow))
         {
             rigidbody.AddForce(Vector3.right * speed);
         }
         if(Input.GetKey(KeyCode.LeftArrow))
         {
             rigidbody.AddForce(Vector3.left * speed);
         }
         if(Input.GetKey(KeyCode.UpArrow))
         {
             rigidbody.AddForce(Vector3.forward * speed);
         }
         if(Input.GetKey(KeyCode.DownArrow))
         {
             rigidbody.AddForce(Vector3.back * speed);
         }
     }
 }