First thing we're going to do is sew the zipper on to one of the flaps. You can just center the zipper along the flap. Don't try to line up the end, it will only make it more complicated later. Centered inconveniently is what we're going for here. Sew it in, getting the flap lined up as close to the zipper teeth as possible, then go back and whip stitch the bottom (non-toothed) edge to the flap as well so that the zipper lies nice and flat against the bag. The picture is what the inside should look like, with the two rows of stitches.
Pin the other flap in place, along the other side of the zipper, and then stitch it down the same way you stitched the first side. It will be a little less fun than the first side, because you'll have to unzip the zipper in order to do the stitching. That's why it's important to pin it in place before you start.
Now you can zip the top closed! Yippee! You're in the home stretch now, so why don't we stitch the zipper closed at the bottom of the flap? It's easy, just stitch over the teeth where the flap ends. Go over it with doubled thread, three or four times. Then slide the zipper pull into the area between the flaps and pin the zipper closed at the other edge of the flaps. Stitch the zipper closed at that edge too, which will be a little less neat, and a little bit more difficult, since the zipper is open at that edge. I've put two pictures, one so that you can see how it should look, and then one pointing out the exact places you will be sewing across the zipper teeth.
Now you're going to cut the zipper off at the end of the flap! Sounds scary, but it's not. Just snip across the end! Then get out your matches or lighter (Jr. Dynamos, please get help from an adult!) and run a flame along the cut edge to seal it and protect it from fraying. (You will notice the knots left from when I sewed that end shut. I didn't cut through my stitches, lol! We're going to cover the ends of the zipper up in the next step, and I didn't want my knots to show on the inside of the bag.) Make sure you cut and seal both ends of the zipper.
Last step! Get out your yarn needle, and the leftover piece of nylon you had left. Stitch the last 4 stitches along the edge of the flaps together, and then sew the flap pieces to the little open area at the butt end of the zipper. Do it on both sides. Weave the tail ends in about two stitches, and then snip and melt the ends, like you did on Monday.
Voila! You now have an awesome new bag to put your current project in! It looks small, but...
Look at all the stuff it's holding!!! Can you believe it?! It's like the clown-car of bags!!!
Btw, yep, that's a couple of lip balm holders in-the-making... Have you made one yet? What are you waiting for?!