You seem to be working on a much larger resolution than traditional pixel art. I have no idea what is the original resolution for your sprite, what brush size you used, etc. but to give you a reference, the original Mario sprites were like 16x16 pixels. In your drawing, even at 25% the current size, the eyes on that character look to be like 3 or 4 pixels big, which makes it more of a “high res” illustration rather than pixel art.
And it’s not just about drawing without smooth antialiased lines, it’s about placing each pixel with care. I’d recommend you switched to a much smaller canvas and try drawing there. The pixel art you see posted online is usually scaled up (in whole increments, like 200%, 300%, 400% and not 150%, or 225% which would break the aesthetic). Also watch some videos on pixel art fundamentals, there’s lots of popular channels, but this would be a good starting point: Pixel Art Class - What is Pixel Art? - YouTube