When I played my game, the player moved straight up, with me being unable to keep control. Would it be fixed if I removed the code for vertical? And if so how would I change the code so no other problems showed? I also do not know much code or c # so, I may have made a mistake easily fixed.
My game is 2D and all I really care about at the moment is making it move left to right.

This is my code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement1 : MonoBehaviour
{
    private float speed;
    public Rigidbody2D rigidbody;
    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        float horizontalInput = Input.GetAxis("Horizontal");
        float verticalInput = Input.GetAxis("Vertical");

        Vector2 direction = new Vector2(horizontalInput, verticalInput);
        rigidbody.velocity = direction * speed;

        rigidbody.gravityScale = 0;
    }
}