1. Attach a piece of interfaced fabric right sides together (RST) at the center front. I included the measurements in the picture below. Stitch a 1/2" around the CF leaving space at the bottom to clip the corners diagonally. This is important so you don't get a bumpy front when you flip the interfaced piece to the back. The teal is stitching lines. The black are just lines for references where you will fold later.
3. Now, starting with one side, fold it open again and re-fold on the next line out. This puts it back in the middle of the opening where it should be. I tuck under the 1/4" edges and pin them. You will stitch this later. If you look closely you can see the un-folded piece on the left. It is hard to show with this teal color.
4. Do the same to the other side. Pin carefully and topstitch (blue line below) both polo pieces as far down as you can.
5. Fold the bottom of the shirt up exposing the bottom of the placket. Stitch across all layers to keep them in place.
6. I finish off the bottom with my serger. I also sew a box at the bottom so the polot shirt does not go so far down. You don't have to do this but I like to.
Do the rest like you normally do! Ta da! Polo!