I really like the way how you approached the way how to become active in gameDev. Jumping into gameJam is a great way how to learn, finish and get feedback to your work/projects. To your game. Overall I find it as a very solid entry, given your timeframe and experience! It is obvious that there are few loose ends that would be great to patch, but this is a something that basically everyone in the game jam struggles with, so don´t worry too much about that.
The gameplay is intuitive and you know what to do right away. I can imagine that some players might preffer "full-auto" shooting instead of single shots, but it makes sence to have single shots, given the theme (you are a snowman) :).
Another thing would be that I have noticed that your strenght is growing, but the "snow-bullets" do still the same damage. I can see that your intention could be that the snowman is actually getting stronger - not the shots - and once strong enough, the bad guys will stop appearing. But since you have a game with core mechanic of shooting, player could expect that stronger means, that with bigger power, you´ll be able to get rid off the enemies faster. Also this mechanic could potentionaly help you build up the difficulty with the time.
At the very end it seems that the displayed message is incomplete?
And of course some music and sound effect would do a great deal to the atmosphere, and if there should be just one advice from me: next time, no matter the time frame think of the music or some basic sfx. I was the same way in my beginings, the most important was to finish some art and some code = sounds not so much important. But then I saw how much even basic sounds and music can do with such a small entries!
Don´t get me wrong, you did awesome job! You created and finished a game project from scratch! And that is a great achievement!! Really great job done and I will love to see how will your journey continue ;)