in my WPF Application, i have a own created widget (Gantt).

Here is the InitializeUI() in the main Window of Gantt:

private void InitializeUI() {
            canvas = new Canvas
        {
            Background = Brushes.White,
        };

        // Bind canvas width and height to the width and height of the window
        BindingOperations.SetBinding(canvas, Canvas.WidthProperty, new Binding("ActualWidth") { Source = this });
        BindingOperations.SetBinding(canvas, Canvas.HeightProperty, new Binding("ActualHeight") { Source = this });

        // Set the Border as the content of the window
        Content = canvas;

        Gantt gantt = new Gantt();
        canvas.Children.Add(gantt);

        BindingOperations.SetBinding(gantt, Gantt.WidthProperty, new Binding("ActualWidth") { Source = canvas });
        BindingOperations.SetBinding(gantt, Gantt.HeightProperty, new Binding("ActualHeight") { Source = canvas });
}

Here is the layout routine of Gantt:

private void createTreeView()
{
    this.treeView = new TreeView();
    this.treeView.BorderThickness = new Thickness(0);
    this.treeView.Margin = new Thickness(0);
    this.gantt_toolbox = new Gantt_Toolbox();


    this.grid = new Grid();
    // Define column definitions
    this.grid.ColumnDefinitions.Add(new ColumnDefinition() { Width = new GridLength(1, GridUnitType.Star) });

    // Define row definitions
    this.grid.RowDefinitions.Add(new RowDefinition() { Height = GridLength.Auto });
    this.grid.RowDefinitions.Add(new RowDefinition() { Height = new GridLength(1, GridUnitType.Star) });
    this.grid.RowDefinitions.Add(new RowDefinition() { Height = GridLength.Auto });

    this.grid.VerticalAlignment = VerticalAlignment.Stretch;
    this.grid.HorizontalAlignment = HorizontalAlignment.Stretch;

    Grid.SetRow(this.gantt_toolbox, 0);
    Grid.SetColumn(this.gantt_toolbox, 0);

    Grid.SetRow(this.treeView, 1);
    Grid.SetColumn(this.treeView, 0);

    Grid.SetRow(this.mainTimeScrollbar, 2);
    Grid.SetColumn(this.mainTimeScrollbar, 0);

    this.grid.Children.Add(this.gantt_toolbox);
    this.grid.Children.Add(this.treeView);
    this.grid.Children.Add(this.mainTimeScrollbar);

    this.Content = this.grid;
}

My problem is that on the right,there is a difference of like 40 px, because the right button of the scrollbar is not visible.
Also the buttons at the top, at the right one, there is a missing area like 40 px.

I checked with debug and Gantt, Canvas and Grid have all the same ActualWidth property.

What is my fault?