Draw Text on Rectangle - Issue with Windows zoom function

Question

I drawing a rectangle with a dynamic number as a string on it and use it for a windows taskbar icon (overlay icon):

private void DrawOverlayIcon(string queue_count) {

    Bitmap bitmap = new Bitmap(30, 30, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
    Graphics g = Graphics.FromImage(bitmap);
    g.FillRectangle(System.Drawing.Brushes.White, 0, 0, 30, 30);
    Rectangle r = new Rectangle(0, 0, 30, 30);
    StringFormat sf = new StringFormat();
    sf.Alignment = StringAlignment.Center;        // horizontal
    sf.LineAlignment = StringAlignment.Center;    // vertikal
    Font f = new Font("Arial", 14, System.Drawing.FontStyle.Bold);
    g.DrawString(queue_count, f, System.Drawing.Brushes.Black, r, sf);

    IntPtr hBitmap = bitmap.GetHbitmap();

    ImageSource wpfBitmap = Imaging.CreateBitmapSourceFromHBitmap(hBitmap, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());

    _icon_overlay = wpfBitmap;

So far so good. But when a user set up the windows zoom function to maybe 120% or 150% the number becomes so large that it is only displayed as one digit.

Can anyone help?

Thanks a lot.