This is pretty fine for a first game :) one piece of game jam-specific advice I'd recommend is to try and incorporate a scoring system into a game like this! It doesn't have to be anything complicated, just adding 1 to an integer whenever you defeat an enemy, and displaying that to the player. Heck, you could have even just made it output in the console.
I also think it's important to scale the difficulty as time goes on. I'm not sure if the current version of the game had it, since I only played for about two minutes, but it felt like the enemy counts weren't increasing and they weren't moving faster. Again, it doesn't have to be anything complicated; making them spawn slightly more often as time goes on, or making them spawn with a slightly higher speed as time goes on, would really make the game more engaging.