Help with jump script

Hi guys. I’m pretty new to Unity and i started to follow some different tutorials to end up
with a movement script for my ball and a jump script

I just can’t seem to make the jump script work? What am i doing wrong?

Here is a picture of the problem


using System.Collections;

public class Movement : MonoBehaviour {

	public float JumpHeight;
	public float speed;
	
	private Rigidbody rb;
	private float isFalling = false;
	
	void Start ()
	{
		rb = GetComponent<Rigidbody>();
	}
	
	void FixedUpdate ()
	{
		float moveHorizontal = Input.GetAxis ("Horizontal");
		float moveVertical = Input.GetAxis ("Vertical");
		
		Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
		
		rb.AddForce (movement * speed);
	
	if (Input.GetKeyDown(KeyCode.Space) && isFalling == false)
	{
		
	GetComponent.<Rigidbody>().velocity.y = JumpHeight;
		isFalling = true;
	}
}
	
	function OnCollisionStay ()
	{
		isFalling = false;
		
	}
}

well, it looks like as soon as it starts to jump… you tell it, … its falling… and in turn its not allowed to be jumping^^