I think that the fabric is light enough to warrent lining the apron as it seems to lack the necessary whatever to stand straight on its own.

Judging by the lines on the edge of the kilt you are flaring it quite a lot - I think too much and the edge of the apron should be reshaped so that the lower part is straight. It would then be more inclined to hang straight.

Being narrower would also help to keep the apron straight, as wrapping a piece of fabric more than half way around your circumference with no darts for internal shaping is asking a lot of any fabric. A greater length of pleats means more opportunities for shaping the garment for a better fit.

Anne the Pleater :ootd: