Hand rolled edges make your scarf more fluid and drapey than a scarf that has machine sewn edges. It can be a time consuming job, but not all that difficult once you get going.
It is best to use a thin needle (a too-thick needle might pucker your fine scarf fabric) and a light weight thread. I am using a large-ish needle here and a strongly contrasting thread so that you can more easily see what is being done.
To Start off
Thread your needle, and put a small knot in the end of it, to hold the thread in place when you start.
With the wrong side of your fabric facing you, fold the top of the fabric over about half a centimetre, and starting about half a centimetre in from the edge of the fabric, push the needle up under the fold and out through the top of the fold.
Pull the thread through until the knot catches to hold it in place. Then, continue as described below.
Go vertically down, just underneath the raw hem, and pick up a small stitch from the scarf body, i.e. from one layer only.
Go vertically up, to the top of the fold: put the needle down into the top of the fold, and take it along about half a centimetre, before coming out through the top of the fold again.
Repeat these two steps, pulling the thread through but not pulling it tight until you have gone across that edge of the scarf. (You can pull the thread tight earlier if you like, but it can make it harder to work an even edge if you do this too frequently).
Finish at the corner, with your needle having come out on the top fold of the scarf edge, about a half of a centimetre in from the edge.
Draw the thread through tighter (but not too tight). As you do so, the edge of the scarf will roll.
Smooth along the rolled edge with your fingers to ensure you have not pulled the thread too tight.
Turn the corner
Make sure the rolled hem is rolled exactly as you want it to be right up to the edge of the scarf, and put a small stitch to hold it firmly in place.
Push the needle up through the fold, from the hemmed edge up through the top of the fold.
Pull the thread through.
Fold over the next side by about half a centimetre.
Go vertically down, just underneath the raw hem, and pick up a small stitch in what is the rolled hem of the side you have just completed, starting at the top edge of that hem.
Go vertically up, at the top of the fold: put the needle down into the top of the fold, through one layer only, and take it along about half a centimetre, before coming out through the top of the fold again.
Carry on as before a couple of times before drawing the thread through to make sure your corner works as it should. You should see a nice neat, square corner.
If you are happy with your corner, carry on as before to the next corner. Otherwise gently unpick the corner and try again.
When you have finished hand rolling your scarf edges, you can lightly iron those edges to make them even more flat and neat.