Try starting on another piece of scrap fabric,then butt it up to the scarf fabric,so that when it finishes on the scrap it should just continue to the scarf.
Clear as mud,right.
Kathi

This is a rolled hemmer foot, right? I start by folding and finger pressing the starting edge of the hem. Then put it under the presser foot flat - don't try to get the roll into the foot's curl yet. Holding the thread tails behind the foot, sew a few stitches, then stop with the needle down.
Raise the presser foot and work the fabric into the curl of the foot. It may take a bit of practice to see how to hold the fabric so that it will feed successfully into the foot and stitch properly.