It looks like you took a pixel art piece and then enlarged it a weird amount, making some "pixels" be 1x2 or 2x2, and some 1x1. This mix of sizes and aspect ratios makes the whole thing look like a mess, and undermines the work you did in placing those pixels. When enlarging, always enlarge by multiplying (2x, 3x...). If you want a different pixel aspect ratio, some programs support them natively, or you can enlarge by setting different multipliers for the height and width (e.g. 1x height, 2x width).

It's hardly ever a bad idea to submit at 1x :] The site has a zoom feature, afterall. With a piece this large, even 2x isn't needed.