100% means without zooming in, i.e. one pixel in the image is one pixel on the screen.
I think more than your choice to make a large pixel art, the problem is the composition, which is making that space feel wasted. This was a problem even in your sketch, which was not pixel art. Nothing in the composition clearly dominates size-wise:
Nothing leads the eye to the important parts of the image, except the character's gaze. All the lines are horizontal and vertical and at best do nothing at all, and at worst lead the eye off the image. The character is looking to the left, which directs the viewer there as well, but the thing in the jar they're looking at has lower contrast than other, less-important elements in the image, so the viewer is likely to skip it.
The animated elements also don't help. You seem to have animated whatever you could, rather than what would help the image as a whole.
What are the important elements in this image? What is the mood you want to establish? What's the story you want to tell?
Here's one example of the same scene with a more interesting composition in the same canvas size/shape. However, it probably tells a different story from what you wanted, since I don't know what you wanted:
Here, the orange blob draws the viewer's initial attentntion, both because it's highest-contrast element (and glowing and lighting up the character) and because it's the largest single object. The character is technically larger, but their face is smaller. Because the character feels a bit smaller than the blob, it makes them look "weaker", perhaps afraid of the blob, or perhaps just not knowing much about it.
The fish-eye perspective also creates tension and a feel of uncertainty/weirdness, and allows the various foreground elements to frame the piece (keeping the eye from "escaping") and allows the background elements lead the eye to the character and the blob.
This composition has a clear foreground, midground, and background, which gives it depth, which also looks more interesting than just having objects float in 2D space with no apparent 3D structure.
You don't need "fancy" complicated perspective like fish-eye to have an effective composition, but you almost always need
something. A completely flat look tends to look, well, completely flat. That can be effective in communicating loneliness if the character is small and the empty spaces are vast, and it can be effective for communicating oppressive orderliness if there are repeating elements (and again, the character is small), but for most stories/moods, you'll want something less flat.