When you have a mat used to create a fine border, it can be difficult to select on the page preview or the page editor if you want to edit it.
The easiest way to do it is from the main screen click the Queue tab and select the mat you wish to edit from the list.
See screen shot below showing the fine mat border around the image as selected.

Oh yes, I did print this cropped image on A3 at 213 ppi, no worries, feather detail is terrific!  

Terry