In my career I have spent hundreds or thousands of hours working on various projects that never amounted to a deliverable product such as a paper, awarded grant, course, talk etc.; any other academic would say the same. I don't list any of this work on my CV, and neither should you. That doesn't mean that I don't think working on such projects has given me valuable experience -- it absolutely has, and it is that experience that has helped me achieve actual, demonstrable successes, which I do list on my CV.
Your CV is the advertising space where you get to use the limited attention you are likely to get from potential employers and colleagues to draw attention to your talent and successes. Using that limited attention to point out something you did that first of all (as David Richerby observed in his answer) isn't that big of a deal, and second of all did not end up having any impact, is counterproductive. Tout your actual successes, and quietly use the experience you gained from preparing the course "behind the scenes" to improve your skills and abilities and make those actual successes greater and more numerous.