I'd be careful. When I did this video...
I was snugging down the center rails and I thought "There is no way that this is tight enough. I should tighten it a little bit more… and maybe a little bit more…"
When I removed the cover to sell the truck, I realized that I snuggled it WAY too much, and the top plastic bed rails were a little wavy. Keep in mind, that the crossbars that you use to lock the cover down also provide support and orientation. If I were to do it again, I would follow their directions to the letter and if I found that the cover skewed a bit here or there, I would then snug it just a little bit more...but not too much. There are multiple securing points of the cover above and beyond the center rail.