C# scrolling panel causes dynamic control rows to have spaces in between

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C#

This question has been asked and answered, probably many times over. I create dynamic controls that make one single row in a panel each time I hit a button. When I create enough rows to make the scroll bar appear it creates a gap in my rows after scrolling down. Below is my code for one of the controls that I add to the form. Any suggestions on what to add or change in this piece?. I understand that I will probably have to add the update to each control.

#region Dynamically Added Controls
    private void addChkItem(string pnType)
      {
        int leftOffset = 7;
        int topOffset = 6;

        if (pnType == "Add-On") // Bundle Panel
          {
            // Create textbox for Qty
            CheckBox chkAddItem = new CheckBox();
            // Position textbox on screen
            chkAddItem.Left = leftOffset;
            chkAddItem.Top = topOffset + AddOnRows * VERTICAL_OFFSET;
            // Set the size of the textbox
            chkAddItem.Width = 15;
            chkAddItem.Height = 14;
            // Name the new control
            chkAddItem.Name = "chkAddItem" + AddOnRows;
            //txtQtyBundle.Text = txtQtyBundle.Name;
            // Mark control for deletion
            chkAddItem.Tag = "Dispose";
            chkAddItem.Enabled = true;
            pnAddOn.Controls.Add(chkAddItem);
            }
        }

What I have tried:

I have tried certain solutions to this problem but the code being adjusted is different than what I am using. I am not experienced enough to solve this issue.