You're most likely holding down too long after the first backflip, causing you to be too close to the warp. Or you are press A too late after pressing down, causing you to move before the backflip. Either way, just make sure you are pressing the A button and down on the stick at about the same time.
If it's not that you're lining up with the wall wrong.
If it's not that you're lining up with the wall wrong.
