Ok, Take what I say with a grain of salt as I'm no proffesional; Maybe try turning the sleeve inside and "curling" the cuff inwards with the iron.
It could also be that the cuff is too "pointy", it's happened to me on a couple vest I've made where the point was too sharp and it started curling outwards. Even though vests are entirely different from cuffs, I think the same "science" is relevant. I say this because it seems like the cuff is slightly skewed towards the underarm.
Put a damp rag on it and put the hot iron it. Some cloths the bottom layer will shrink.
Otherwise, take the seam apart and hand sew it so it slightly rolls in. Don't want the roll noticeable to the untrained eye.
It's a smart looking coat.
It's a very handsome coat. I wouldn't let it bother you.
Could also been caused when you sewed in the buttonholes. The under cloth was pushed out towards the cuff.
Is it on both sides?
If its only on one side, it's probably caused by how you stitched the corner.
The inside should be sewn short on the inside so it doesn't curl out.
50/50 linen wool blend
Is the cloth linen or wool?
Only commenting to say that I have this issue too sometimes. Just an idea, could it be that the lining is too loose?