Using terrain.sampleheight() with matrix4x4.tr

Hello,
I am trying to draw some grass using Graphics.DrawMeshInstanced() and it works, but now i want it to spread all over terrain. But here is my problem. I can not figure out how to use the Terrain.SampleHeight().
Bellow i will post the entire code so you can check for yourselfs.
If you can help with the rotation as well, that would be great.
Thank you.

<pre>using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class GrassInstancing : MonoBehaviour
{
    public int Instances;
    public Mesh mesh;
    public Material[] Materials;
    private List<List<Matrix4x4>> Batches = new List<List<Matrix4x4>>();
 
    public Vector3 eulerAngles;
 
    public Terrain terrain;
    public float yOffset = 0.5f;
 
    private float terrainWidth;
    private float terrainLength;
 
    private float xTerrainPos;
    private float zTerrainPos;
 
    private void RenderBatches()
    {
        foreach(var Batch in Batches)
        {
            for(int i = 0; i < mesh.subMeshCount; i++)
            {
                Graphics.DrawMeshInstanced(mesh, i, Materials[i], Batch);
            }
        }
    }
 
 
 
 
    // Update is called once per frame
    void Update()
    {
        RenderBatches();
    }
 
 
 
     // Start is called before the first frame update
    void Start()
    {
       
 
        //Get terrain size
        terrainWidth = terrain.terrainData.size.x;
        terrainLength = terrain.terrainData.size.z;
 
        //Get terrain position
        xTerrainPos = terrain.transform.position.x;
        zTerrainPos = terrain.transform.position.z;
 
FROM HERE STARTS MY PROBLEM
        //Generate random x,z,y position on the terrain
        float randX = UnityEngine.Random.Range(xTerrainPos, xTerrainPos + terrainWidth);
        float randZ = UnityEngine.Random.Range(zTerrainPos, zTerrainPos + terrainLength);
        float yVal =Terrain.activeTerrain.SampleHeight(new Vector3(randX,0, randZ));
 
        //Apply Offset if needed
        yVal = yVal + yOffset;
 
        Quaternion rotation = Quaternion.Euler(eulerAngles.x - 50, eulerAngles.y, eulerAngles.z);
 
 
        int AddedMatricies = 0;
        Batches.Add(new List<Matrix4x4>());
 
        for(int i = 0; i < Instances; i++)
            {
                if(AddedMatricies < 1000)
                {
                    Batches[Batches.Count -1].Add(Matrix4x4.TRS(new Vector3(Random.Range(xTerrainPos, xTerrainPos + terrainWidth),
                        yVal,
                        Random.Range(zTerrainPos, zTerrainPos + terrainLength)), rotation,
                        new Vector3(Random.Range(1, 3),Random.Range(1, 3), Random.Range(1, 3))));
                        AddedMatricies += 1;
                }
                else
                {
                    Batches.Add(new List<Matrix4x4>());
                    AddedMatricies = 0;
                }
            }
 
        Debug.Log(yVal);
    }
}