Dear Tx,
I guess I don't understand. If you've finished the armholes and neckline, why do you still have raw edges? Or, have you not completed the edging? This is how I had my students do it. Use a zigzag stitch--the multiple zigzag is best for this. Sew the inside first; fold the trim to the outside, then turn it under, and stitch it again. If any trimming needs to be done, it should be before you finish the second side.
When I use trim for the edge, I cut the seam allowances to the exact width I want the trim to be when finished. This makes it easy to fold over the edge and get it even all the way around.
Teri
P.S. Duck-bill scissors are great for trimming. They're razor sharp, and you can use the bill next to the fabric so you can't cut the garment.