Although I have not hemmed an already made kilt, I have remade quite a few now as I am working at getting smaller around the middle.

I find that it makes it a lot easier to impose new shapes onto material if I remove the old pressing so I am starting without unwanted folds, and pressing in the new folds makes sewing them much simpler.

I'd suggest pressing out the fold at the bottom of the kilt, then turning up the edge and pressing it before you start to sew it, then once sewn, press the lower edges of the pleats.

Be careful with man made fibre fabrics, you need the iron only just hot enough to do the work, and use a pressing cloth when working on the right side of the material.

Most tailoring seems to rely heavily on skillful pressing and shaping rather more than sewing.