First of all thanks for playing and rating our game.
The game native resolution is 84x48 as per the requirements.
Just as most jam entries (yours included ;-) ) the window is just scaled by 10 to allow the player to play more comfortably the game.
You will first have to build your project without scaling at 84x48 pixels.
Then you will need to open the index.html. Inside you should see a <style> tag somewhere. Inside that tag there should be a line that says: #canvas {
...
}
Add the following code inside the canvas.
transform: scale(10, 10);
transform-origin: top left;
image-rendering: pixelated;
And that should do the trick. If there it doesn't work then send me a screenshot and I will check it out.