How can I "lock" a LineRenderer and make it only follow one direction?

Question

So I have two predetermined points and I want to draw a line between them.

I don't have an issue with actually drawing the line or snapping it to final position, but I want to lock it in between the two points while it's drawing. At the moment, it follows my touch's position in all directions.

Here's what it currently does:

Here's an approximation of what I'm trying to do (finger still on screen):

And here's how the line looks when it connects with the final point (finger has been lifted and line is still drawn):

    public class Path : MonoBehaviour
{
    [SerializeField] private Vector3[] positions;

    [SerializeField] private GameObject child1, child2;

    private Vector3 startPos, currentPos, endPos;

    [SerializeField] private bool _firstChildSelected = false;
    [SerializeField] private bool _secondChildSelected = false;

    [SerializeField] private LineRenderer line;

    Vector3 direction;

    Touch touch;

    // Start is called before the first frame update
    void Start()
    {
        positions = new Vector3[4];
        endPos = child2.transform.position;
    }

    // Update is called once per frame
    void Update()
    {

        if (Input.touchCount > 0)
        {
            touch = Input.GetTouch(0);
            RaycastHit2D hit = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(touch.position), Vector2.zero);


            if (touch.phase == TouchPhase.Moved || touch.phase == TouchPhase.Stationary)
            {
                if (hit)
                {
                    // If it collides with the first checkpoint for the first time...
                    if (hit.transform.gameObject == child1 && !_firstChildSelected)
                    {
                        positions[0] = child1.transform.position;
                        line.SetPosition(0, positions[0]);
                        line.SetPosition(1, Camera.main.ScreenToWorldPoint(touch.position));
                        _firstChildSelected = true;

                    }

                    // If it collides with the second checkpoint for the first time, and already passed by the first one... 
                    if (hit.transform.gameObject == child2 && _firstChildSelected && !_secondChildSelected)
                    {
                        _secondChildSelected = true;
                    }
                }

                // Follow the touch.position until it reached the final position...
                else if (_firstChildSelected)
                {
                    currentPos = Camera.main.ScreenToWorldPoint(touch.position) + new Vector3(0, 0, 10);
                    direction = (endPos - positions[0]).normalized;
                    line.SetPosition(1, currentPos);

                }

                // When both have been selected, lock the line in
                if (_firstChildSelected == true && _secondChildSelected == true)
                {
                    currentPos = child2.transform.position;
                    line.SetPosition(1, currentPos);
                }
            }

            // Clear all on finger lift, but keep the line drawn
            if (touch.phase == TouchPhase.Ended)
            {
                Array.Clear(positions, 0, positions.Length);
                _firstChildSelected = false;
                _secondChildSelected = false;
            }
        }
    }

I know my code is messy, I'm kinda new to all this and I've been trying out some stuff. Any help would be appreciated!