Wrong placing for background

Hi. I need to make an endless background. I tagged all my backgrounds with the tag 'Background' and created an empty game object, which will, when collides with the background, perform this code:

             background_width = ((BoxCollider2D)target).size.x;
 
             // we create a new position for the just touched background
             Vector3 newPosition = new Vector3(lastBackgroundX + background_width, target.gameObject.transform.position.y);
             // chanes its position to the new one
             target.gameObject.transform.position = newPosition;
             // change the lastBackgroundX so that we will be able to find a new position for the next background
             lastBackgroundX = newPosition.x;

Well, this code simply works not as it should. Instead of putting background one after another, my code, I don't know why, puts next background at a ridiculous distance from the previous one. So there is no 'endless background' effect. What should I do?

P.S: value to the lastBackgroundX is assigned at the start of the game, my scripts finds the farthest object with the tag 'Background' and assigns its transform.position.x to the aforementioned variable.