Place the remaining main fabric piece in front of you, and then place the zip down on top once more with the zip facing downwards and the unused edge lining up with the top raw edge.
Next, add the remaining lining piece on top, right side down, and top raw edge matching the zipe edge and top edge of the main fabric.
Pin, tack and then machine stitch in place using your zipper presser foot.
Once stitched, fold the main and lining pieces on the second side back so that the zip can be seen between the two main fabric pieces and the two lining pieces. Press with your iron.