How can i make my 2D character not toppling over

Hello i am making a 2D game where my character is running to the right side over the screen and when he starts running he is falling over and my character is moving to the right side over the screen on his stomach i've tried a lot like freeze the z rotation and when i do that i can't jump with him maybe i made a mistake in my script i dont know pls. help me

here is my script:

using UnityEngine; using System.Collections;

public class PlayerScript : MonoBehaviour { public float maxSpeed = 10f; public float jumpForce = 700f; public bool grounded = false; public Transform groundCheck; private float groundRadius = 0.2f; public LayerMask whatIsGround;

 void Update () 
 {
     grounded = Physics2D.OverlapCircle(groundCheck.position, groundRadius, whatIsGround);
     GetComponent<Rigidbody2D>().velocity = new Vector2 (1 * maxSpeed, GetComponent<Rigidbody2D>().velocity.y);

     if (grounded && Input.GetKeyDown (KeyCode.Space)) 
     {
         GetComponent<Rigidbody2D>().velocity = new Vector2(GetComponent<Rigidbody2D>().velocity.x, 0);

         GetComponent<Rigidbody2D>().AddForce(new Vector2(0, jumpForce));

     
     }
 }

}