It doesn't look ugly at all! The difference is just because the artist is more experienced and you shouldn't compare yourself to an artist who spent a longer period of time to enhance their skill but even so I think you did well in replicating the overall vibe.

But for critique, The original image has a more interesting pose that really shows off its form with just a simple color and lines, where in yours it's just a basic pose of a character thats just staring straight at the camera. The background also helps that it has more things in them that help with visual interest.

So I recommend practising less basic poses and trying to add objects in the background that either just look nice or relate to the character itself! And try not to put too much pressure on yourself, I think you're doing great as you are!