RectTransform size aspect ratio

I try to have different panels outside the screen, adjusted to the center panel.

But when the resolution changes, for example in 800x480, some gaps appear between the panels.

My intention is to make the panels fit tightly and make them slide without interfering with each other, but I can't do it without having the correct starting coordinates.

 public RectTransform mainPanel, rightPanel, leftPanel, topPanel, bottomPanel;
 
 
     public Vector2 centerPosition, rightPosition, leftPosition, bottomPosition, topPosition;
 
 
 
     void Awake()
     {
 
         // Assign position to each panel
         centerPosition = new Vector2(0f, 0f);                       // Center
         rightPosition = new Vector2(mainPanel.sizeDelta.x, 0f);     // Right
         leftPosition = new Vector2(-mainPanel.sizeDelta.x, 0f);     // Left
         topPosition = new Vector2(0f, mainPanel.sizeDelta.y);       // Top
         bottomPosition = new Vector2(0f, -mainPanel.sizeDelta.y);   // Bottom
 
         // Move the panels to their starting positions
         mainPanel.DOAnchorPos(centerPosition, 0f);
         rightPanel.DOAnchorPos(rightPosition, 0f);
         leftPanel.DOAnchorPos(leftPosition, 0f);
         topPanel.DOAnchorPos(topPosition, 0f);
         bottomPanel.DOAnchorPos(bottomPosition, 0f);
     
         
     }