I do not have experience with drawing Tiled maps using Extended, but I have my custom code to draw my tiles in combination with TiledSharp. But how I do it is as follows: I multiply my map height and width of each tile with the game's scale, which in your case is 2. Then I scale up each individual tile when I draw them in the SpriteBatch by passing the scale in there.
For further assistance, it would be useful if you could share your current code with us. But I hope this reply has helped you.