A question?

I've a modern quilt loaded on my longarm and was going to do a quilting panto with lots of straight lines. I designed this one myself and do not have the software for the machine to just do it for me. The photo shows two rows.

I tried a few inches and had to unsew it because what seemed straight with the laser was impossible wavy. It looked awful and I had to pick it out. 

Having never marked a quilt already on the machine, does anyone have any tips? I've made a stencil and could use chalk, then quilt it with a ruler, but this could take forever. Is there any way to do this that will not give me a headache and a sore back?

I could change the quilt pattern, but it is perfect for the quilt... and maybe I'm just a little proud of myself for coming up with it? Sigh!