Icons always draw at the system default icon size. To display a zoomed view of an icon image, copy the icon image to a bitmap, then use the TCanvas.StretchDraw method. Example:

procedure TForm .Button Click(Sender: TObject);
var
  TheBitmap : TBitmap;
begin
  TheBitmap := TBitmap.Create;
  TheBitmap.Width := Application.Icon.Width;
  TheBitmap.Height := Application.Icon.Height;
  TheBitmap.Canvas.Draw(0, 0, Application.Icon);
  Form .Canvas.StretchDraw(Rect(0,
                                0,
                                TheBitmap.Width * 3,
                                TheBitmap.Height * 3),
                                TheBitmap);
  TheBitmap.Free;
end;