I can see you tried to address the limitations, but the thing is, if you take a screenshot of the game, scale it down to 84x48 and then back up, it doesn't look identical. This is an easy way to test if your game's resolution is actually 84x48.
What I do when scaling up windows in Godot like this is I keep the window width and height at the minimum resolution (84x48 in this case), but the test width and height (a bit lower down in the project settings) to the scaled-up resolution (840x480 in your case) - there might be a better way of doing this, but it works for me. (Another suggestion for future jams - export a Web version! Those get more attention because they're easier to get straight into playing.)
Another thing I noticed is that your sprites are blurry (and would be even more blurry at 84x48), which can be simply fixed by selecting your sprites, selecting "import" next to the "scene" tab, turning off "filter" and reimporting.
Yeah, I get the time issue. Sorry, I just like to give criticisms when giving feedback because I think it helps to know what you could've improved, as opposed to just hearing "well done" - I hope I was being constructive.