For some reason I am not sure why, but the turtle draws shape object lines that lie on top of the background layer. So you do need shape ellipses to draw on top of the turtle path. Each shape will appear on top of the last - it is also possible
to alter the layer (Z indez) of shapes using extensions, but in your case drawing the ornaments after the turtle has drawn its shape will work ok.
The GraphicsWindow.Draw.. and GraphicsWindow.Fill... commands draw fixed objects on the background layer below any movable shapes created using the Shapes or Controls methods.
In order to position a shape ellipse you need to use Shapes.Move, this positions the named shape (returned when the shape is created) setting the top left corner of the shape bounding box, therefore the centre is at (left+width/2,top+height/2).
Here is a simple example positioning shapes (Circles of radius 20) on mouse clicks.
GraphicsWindow.MouseDown = OnMouseDown
Sub OnMouseDown
xM = GraphicsWindow.MouseX
yM = GraphicsWindow.MouseY
GraphicsWindow.PenWidth = 0
GraphicsWindow.BrushColor = "Red"
shape = Shapes.AddEllipse(20,20)
Shapes.Move(shape,xM-10,yM-10)
EndSub