for(int y = 0; y <= amp + 3; y++)
{
    for(int x = 0; x <= chunkSize - 1; x++)
    {
        for(int z = 0; z <= chunkSize - 1; z++)
        {
            if(Physics.CheckSphere(new Vector3(Mathf.Round(x),Mathf.Round(y),Mathf.Round(z)),0.5f) == false)
            {
                Instantiate(grass,new Vector3(x,y,z), Quaternion.identity);
                dontPlaceHere.Add(new Vector3(x,y,z));
            }
        }
    }
}
}