Continue reading to see how to do this.

Fold the bias strip in half and press. I used 3" but I htink that was a bit wide for only a 1/4" seam. You ideally want your strip to be 6x the finished binding width.

Keeping bias strip folded, pin in place on the right side, raw edges together. Here I'm doing both the straight and curved edges at the same time. For the curved edge, I pressed the bias strip to a curve so it would pin nicely.

On the curved part, I topstitched. On the straight part, I stitched in the ditch. You could also hand slip stitch it on the back.
Note: A double bias binding is also called a French binding sometimes.