What if you used a tripod mount as an anchor on camera. Tie string to the tripod mount on one end and the other to a branch or swing set. This way you'll get straight lines with no broken glass.
I'm not a Pro, but looks like ISO could stand to be a bit higher than 400 or bump down to a little slower shutter speed. Past that, all I can say is try, try again.
Like the tracks and the U P photos. As for putting your camera on the tracks, well unless you use one that is designed to take a vibration like none other, then I wouldn't sugest it.
Much better. It's little different crop than I imagened, but it works. I think your crop tells a better story to me. The real question is = Do you like it? SJ