Ok, take your ladder run in ramp thing & connect the 2x4's so they are straight.
Here are a couple pics, one is how you have it drawn & the other is the way it needs to be.
Then once that is straight, finish it like your drawing, except don't add the plywood skin over top of the ladder run in ramp thing.
Leave spaces in it, just wide enough so that the front of your board doesn't get caught in the rungs, the fewer the better. Less drag.
Now you are ready to rock.
That's still gonna break. If you want to go the route that I think Timmy is suggesting and take the middle transition out of the ramp, then make your ramp one piece. And be sure to turn the 2x4's that the "ladder rungs" screw to so that the longer side of the wood (the 4 inch length) is pointing downward, perpendicular to the ground. I like his idea about getting rid of the plywood. It's not needed and will save you money on this project.