Adding speed relative to move vector (Rigidbody2D)

Hi,
i’m currently working on a arcanoid clone and have a problem:

What i want: To increase the speed of my ball relative to it’s movement-vector.

What i tried: A LOT. I crawled through so many answers here but got nothing to work.

Here is what i have:

using UnityEngine;
using System.Collections;

public class Ball : MonoBehaviour
{
    public bool hasStarted = false;
    public bool tweaked;
    public bool speedTweaked;
    public float speed;
    public Vector2 thrust = new Vector2 (0.5f, 0f);
        
    void Update ()
    {
        if (!hasStarted) {
            if (Input.GetMouseButtonDown (0)) {
                hasStarted = true;
                rigidbody2D.velocity = new Vector2 (3f, 10f);
            }
            if (!speedTweaked){
                rigidbody2D.AddRelativeForce(thrust); // Does nothing lol
                Debug.LogError("uhm..");
            } else if (speedTweaked) {
                rigidbody2D.AddRelativeForce(thrust); // Does also nothing omg
                Debug.LogError("ok...");
            }
        }
    }
    
    void OnCollisionEnter2D (Collision2D col)
    { 
        //add some randomness - this is also the cause of speed loss/ gain
        Vector2 tweak = new Vector2 (Random.Range (-0.2f, 0.2f), Random.Range (-0.2f, 0.2f));
    
        if (hasStarted) {
            speed = rigidbody2D.velocity.magnitude;
            Debug.Log (speed);
            
            if (!tweaked) {
                rigidbody2D.velocity += tweak;
                Debug.Log ("Tweaked");
                tweaked = true;
            } else {
                rigidbody2D.velocity -= tweak;
                Debug.Log ("Tweaked");
                tweaked = false;
            }
            
            if (speed <= 11) {
                Debug.LogError ("Speed is under 10");
                speedTweaked = false;    
            } else if (speed >= 12) {
                Debug.LogError ("Speed is over 12");
                speedTweaked = true;
            }
        }
    }
}

I would appreciate some ideas.

Greetings

i figured out myself:

void AdjustSpeed ()
	{
		speed = rigidbody2D.velocity.magnitude;
		
		if (speed < 11) {
			rigidbody2D.AddRelativeForce (rigidbody2D.velocity.normalized * 10);
		} else if (speed > 11) {
			rigidbody2D.AddRelativeForce (rigidbody2D.velocity.normalized * -10);
		}
	}