textblock not wrapping when set in code behind in background agent

Question

I'm making a custom image in a background agent on Windows Phone 8 to display on the back of my live tile. I've hit a small problem, I cannot get my text wrapping to work.

I first create a canvas, which then holds the textblock. I've tried putting a stackpanel in between but no luck. I set TextWrapping to Wrap, I set (max)height & (max)width on all elements but no luck. I've also tried setting trimming to none.

Here's the code:

        private void UpdateAppTile(string message, int stuntCount)
    {
        System.Threading.ManualResetEvent mre = new System.Threading.ManualResetEvent(false);

        Deployment.Current.Dispatcher.BeginInvoke(() =>
            {
                var can = new Canvas();
                can.Background = new SolidColorBrush(Color.FromArgb(255, 255, 204, 0));
                can.Width = 336;
                can.Height = 336;
                can.MaxHeight = 336;
                can.MaxWidth = 336;
                TextBlock textBlock = new TextBlock();
                textBlock.FontSize = 26;
                textBlock.Foreground = new SolidColorBrush(Color.FromArgb(255, 51, 102, 153));
                textBlock.TextWrapping = TextWrapping.Wrap;

                textBlock.Padding = new Thickness(10,10,10,10);
                textBlock.MaxHeight = 336;
                textBlock.MaxWidth = 336;
                textBlock.MaxHeight = 336;
                textBlock.MaxWidth = 336;
                textBlock.TextTrimming = TextTrimming.None;
                textBlock.Text = message;
                StackPanel stackPanel = new StackPanel();
                stackPanel.MaxHeight = 336;
                stackPanel.MaxWidth = 336;
                stackPanel.MaxHeight = 336;
                stackPanel.MaxWidth = 336;
                stackPanel.Children.Add(textBlock);
                can.Children.Add(stackPanel);

                const string liveTilePath = "/Shared/ShellContent/live_tile.jpg";

                var writeableBitmap = new WriteableBitmap(336, 336);
                writeableBitmap.Render(can, null);
                writeableBitmap.Invalidate();

                using (
                    var isoFileStream = new IsolatedStorageFileStream(liveTilePath, FileMode.OpenOrCreate,
                                                                      IsolatedStorageFile.GetUserStoreForApplication
                                                                          ()))
                {
                    writeableBitmap.SaveJpeg(isoFileStream, 336, 336, 0, 100);
                }

                ShellTile appTile = ShellTile.ActiveTiles.First();
                if (appTile != null)
                {
                    FlipTileData tileData = new FlipTileData
                        {
                            BackBackgroundImage = new Uri("isostore:" + liveTilePath, UriKind.Absolute),
                            BackContent = "",
                            Title = "Set at " + DateTime.Now.ToShortTimeString()
                        };
                    tileData.Count = stuntCount;
                    appTile.Update(tileData);

                }
            });

        mre.WaitOne();
        NotifyComplete();
    }

I also have a small problem with sometimes the image not finishing rendering/saving on time and the tile showing an older version, but I'm still looking at that.

Thanks !

Jorn