So you make it to the third lever-moved platform, but can not get to the ledge with the final lever? That should be the easiest jump of that part (the jump to the first platform being moderately easy, with the ones from the first to second platform and second to third requiring a bit of timing and coordination).
Hit each of the levers a few times, and make sure the three platforms each end up in their middle height positions, forming a stair like configuration up to the final ledge.
