This is a tutorial on neckline with bias strip. Make a bias strip from this tutorial. Fold it in half width-wise. Place this strip along your cut neckline.
Secure this bias strip with pins with the right sides facing together in this figure below. (the raw edges are to be kept together towards the neck line)
Sew it along the neckline. Invert it towards the wrong side. Rest of the method is similar to the one described in the tutorial on stitching neckline'
To end, don't forget to hem/machine stitch the edges. That's it!