This is quite a profound take on the theme, especially coming from a 15 year old game developer (assuming the info in your profile is up to date). The platformer mechanics, though simple, do their job of exploring the theme perfectly well, with your level even going as far as offering multiple paths and endings. I like how the pits and invisible walls, the latter of which you occasionally place behind the player, help to express the idea that quite often the choices one makes in life are irreversible.
What few technical and gameplay issues there are have already been mentioned by previous commenters, so I won't dwell on them.
The audio and visuals come together to create a mood, which I would describe as thoughtful and somewhat tense (time is ticking) at the same time. This aspect of your game, I feel, is very strong.
I think the risk you took in using Unity and C#, which you admit is not something you have much experience with, has definitely paid off. The scope for the 48 hours of the Compo was selected wisely: there is nothing obviously missing from your game and no game-breaking bugs either. You even had time to create a custom icon for the game - now that's attention to detail.
My main criticisms have to do not so much with the game itself, as with the way it's presented on the site. Firstly, unless I'm missing something, I don't see a link to the source code anywhere, though I believe it is [required](https://ldjam.com/events/ludum-dare/rules) for Compo entries. You should add a link to your Github repo (or even just a zip with your Unity project) to your game's page, so that there are no problems with the rules.
Additionally, despite using Unity, you only provide a Windows version of your game. Come on. :) I understand why you might decide to not have a WebGL build, since without additional tweaking of the game those often come out laggy and inferior to desktop builds. But you don't have builds for other desktop platforms either. I mean, I mainly use Linux on my laptop and I would've been able to try your game much earlier, if it just had a Linux build, and I'm sure there are even more people on Macs who love to play games. So do upload builds for other platforms as well - the rules allow you to do so after the deadline and your game will be available to more players.
Overall, I think you did a great job. If there's one thing I'd say, it's that you probably shouldn't have much fear of the future, if this entry is anything to go by. In fact, it will be pretty interesting to see what games you come up with in the future.
Good luck!