First of all, thank you for your comment :)
This is the first time I've made a game with just simple shapes like this. I actually drew everything directly in the game engine, which saved me a lot of time! And I'm quite proud of the fact that I was able to suggest the calm and agitation of the aquatic depths with such minimalist graphics.
As for Agar.io, it's perhaps an unconscious inspiration: I played it a lot about ten years ago (time flies!).
If I had three days instead of three hours, I'd try to solve the inevitable problem of this type of game (which is linked to its main quality): The aim of the game is to get the biggest snake possible, and as the snake increases, the game naturally becomes more difficult as there's less and less room to move around. It's a very interesting principle, and one that the original “snake” game exploited perfectly. But there naturally comes a point when the game stops because there's little or no room left. So, with three days ahead of me, I'll try to make the game a little more infinite, because this is the kind of game you can play on the train, in the doctor's waiting room or simply in bed on a chill day.
In short, I think we need to implement a system of upgrade choices (a bit like in hades, or in vampire survivor), which is minimalist but can renew the gameplay and increase the game's lifespan. A few examples of possible upgrades: increase the size of the terrain, attract nearby food to yourself, obtain a kind of shield to protect you once against an unfortunate shock, reduce the size of your body without lowering your score, and so on.
And perhaps in parallel with these improvements, other elements could increase the difficulty: more enemies, different enemies, momentarily forbidden game zones, etc.
The idea, of course, would be to keep things as minimalist as possible, but I think it's possible.
Maybe you'll get to see this version one day, as I'm thinking of making a small mobile application. I just need to find the time in the midst of my other projects.