to turn the fabric under I use a toothpick (am I doing toothpick-turning?). I have the toothpick allways
between my lips so it is allways a little bit wet, that helps a lot to catch the fabric to turn it under .
But that is MY way to do it, I appliqued the Dutch Treat Quilt with this toothpick method and it worked fine for me, it's not my invention, I got this tip on a group who worked on the DT quilt.
It's up to you to turn it with your needle or to give the toothpick a try! :-)