As others mentioned, managed to get it working by zooming in the browser page.
Absolutely love the character sprite, it's very cute. Thought the art was nice across the board too. The collisions were a little wonky sometimes (such as getting stuck against walls, and falling at the edge of platforms). I found being sent right back to the beginning after getting hit pretty harsh too.
Overall, I think this was great for a first game! if you could iron out some of the issues, and refine it some more, it would be really fun.