
Congratulations!
If it works, it works! Good on ya!
You seem to have the basic concept down just fine.
My first few were pretty "sloppy" as well, and it wasn't until the member named Nephiel at EDCforums made a superb specimen and showed the forum a photo that I became aware that what I had made could be improved. (Ya gotta love it.) So I went back and re-made a sling and that's the one you see with the yellow golf ball.
The overall plan for that sling is easy -- I stand by that assessment -- but it is also true that to make a nice neat one with very little as far as gaps in the pouch, there's plenty of "working" the weave that you will have to do. Also, you should know that you will need about 5 feet of cord to do the crossweave in a more dense pattern.
If you make a few more of these, you will start to really "know" the pattern. Once that happens, you will get proficient at reading the pouch and will be able to feed cord back through it to address issues of tightening or loosening the warps to achieve the shape you want. A well-made one of these will retain a cupped shape without difficulty or any kind of seasoning. All you have to do is loosen the "sheet bend" a bit at the ends of the pouch, and tug each of those outer lines that run along the rim of the pouch to shorten them, then tighten the sheet bend again. It ends up working like a drawstring cinching the pouch into a cupped shape.
I'm pleased that people are trying that design out. Best wishes for success with your sling.