The key to a great cuff is ensuring the inner seams are covered and finished off correctly.
Here's how it's done.....
Once the cuff is sewn to the main fabric piece, press your joining seam allowance downwards towards the cuff bottom edge.
Press a small hem along the bottom edge of the cuff.
Fold your cuff upwards towards the seam joining your cuff to main fabric piece.
The main thing to get right here is making sure the cuff folded edge is lined up with your row of stitching.
Sew a small 2/8 seam on the cuff side.
By lining up your folded edge to the stitching line you will get a straight row on the bottom cuff when you turn it over.