I myself have completed this. It took a few attempts to do though. Perhaps, instead of just springing through a plain box, you could give each special stage it's own theme you need to bounce through, if possible. Or even detail the the level at the least if you're going to use the theme you're using now. I like the concept of the spring + 2D. It was a very clever idea and it actually had me playing trying to beat the special stage and have fun despite it's difficulty. Sadly though, this is far too difficult for a first special stage. Perhaps for the earlier special stages, you could have the player bounce for a bit with no rings on the springs to get prepared. Even then, you should let the player be able to get a grasp on where to go to grab rings first, like having them slowly be pushed to the first set of springs.
There's nothing ultimately wrong with the special stage you have here. You can save this completed work for special stage 6 or special stage 7 like Rob suggested.