Scaling InkCanvas strokes to fit specific dimensions to crop out unused space

Question

I am attempting to scale an InkCanvas's contents (Strokes) to fit a fixed page size for printing. I want to essentially crop out all of the surrounding whitespace from the InkCanvas, and scale up the Strokes to fit the page while maintaining aspect ratio.

In the handler below the markup, you can see that I am changing the dimensions of the grid that starts at 800x300, and I'm making it 425x550, half of the size of a printable page.

markup:

 <Grid>

    <Button Height="100" Width="100" HorizontalAlignment="Left" PreviewMouseLeftButtonDown="Button_PreviewMouseLeftButtonDown_1" />

    <Grid Width="1200" Height="1400" Background="Aquamarine" HorizontalAlignment="Right" VerticalAlignment="Top">

        <Grid Background="Red" x:Name="grid" Width="800" Height="300">

            <Viewbox x:Name="vb"  Width="800" Height="300" Stretch="Fill" StretchDirection="Both">

                <InkCanvas Width="500" Height="500" Background="Transparent" IsEnabled="True"/>
            </Viewbox>

        </Grid >

    </Grid>
</Grid>

---

codebehind file:

bool b = true;

private void Button_PreviewMouseLeftButtonDown_1(object sender, MouseButtonEventArgs e)
    {
        if (b)
            {
            //I toyed with using Uniform, UniformToFill, and Fill
            vb.Stretch = Stretch.Fill;
            grid.Width = 425;
            grid.Height = 550;

            //scale viewbox down until it fits horizontally
            var scaleX = grid.Width / vb.Width;
            vb.Width *= scaleX;
            vb.Height *= scaleX;

            //if constraining it to the width made it larger than it needed to be vertically, scale it down
            if (vb.Height > grid.Height)
            {
                var scaleY = grid.Height / vb.Height;
                vb.Width *= scaleY;
                vb.Height *= scaleY;
            }
            b = false;
        }
        else
        {
           //reset it back to what it was
            vb.Stretch = Stretch.Fill;
            grid.Width = 800;
            grid.Height = 300;
            vb.Width = grid.Width;
            vb.Height = grid.Height;
            b = true;
        }