It took me a few times reading that to get the picture in my head, but I understand what you are saying. The backing plate helps to bend the whole bottom of the C channel instead of just the edge.

I was realizing that the hammer was mostly bouncing off, but I'd like to believe it was doing a little bit of good. As thick as the double layer of steel is I wouldn't have thought I could bend it back with a cresent wrench, but it is worth a shot if this is a proven method . One issue with the backing plate is that where the front brackets mount where I'm trying to square it up is curved...maybe if i use a real narrow backing plate it would still prevent bending the lip and keep the curved shape in the rail.

My other solution is to maybe get a cinder block and a bar to pry up on the rail? Again though I'm concerned about the curve of the rail.

CE in the instructions says simply to "square the frame to 90* using a square" I tried beating the frame with the square, but it didn't work