what you do there is called double knitting on straight needles. Pretty neat, actually. I just came across it lately.
Give it a try: Every second stitch on a second needle... then you will have a pocket if you did it right.
your piece is just not an open pocket because the top is connected.
If you did everything right, you have a fabric that is stochinette st on both sides and not connected in the middle.
There is a thread in What'cha knitting! called "Some Small Projects" and there is discussion about this kind of knitting.
Edit: I was too late! But hopefully still helpful.