I cut one large rectangle, in wich the yoga mat will fit. If you want to, you can just cut one large rectangle and a small rectangle, make the strap and attatch it. Then just sew two of the edges of the larger rectangle and put the draw string opening on the other end and you're done. I wanted to do a circular (came out oval) shape to the bottom.
Below are pictures of the parts you need for this project. Further instructions are in the video. Happy sewing and have fun at the gym, friends! :)