If you have the Art of Kiltmaking, go to page 34. I was not able to understand enough of the pictures to descern if you have a deep pleat on the left apron. That is also where the hidden pleat belongs. The underapron, on the right of the pic on pg 34, should have an inverted pleat (also called a box pleat).

Does your kilt match the picture? I also have a tab on that page to refer to when I get confused with left apron and right apron. When you put on a kilt the left hand grabs the apron (left apron), the right hand grabs the underapron (right apron).

Is this how your kilt was made?
Did you strum the pleats?

Hope this helps.