Your pre-zoomed image is at a non-integral zoom, so the pixels are distorted. When you feel you must pre-zoom a pixel art piece, do it in exact multiples (2x, 3x, etc) so that the pixels remain all the same size and shape. Your original piece is 16x16, you could zoom it by 6x to get a 96x96 image with no distortions but hardly any size difference from your 100x100 goal.
Yeah, sorry about messing up :) Can I edit it only after it's approved?