Fun little game! It's quite simple, but it does everything I think it needs to do. I dig your art style too, with the thick black outlines giving everything a sort of cartoon-y pop.
Being able to hold down the mouse to shoot rapidly would be a great addition; my frantic clicking started to be a bit uncomfortable to me, and probably to my trackpad as well after a little while, haha. I also think, if your planning on working on this anymore, if a bit of a difficulty ramp would be nice. Maybe just having spawn rates steadily increase as the game goes on. I know that kind of thing can be hard to balance nicely in a jam though.
Overall, great work! Wouldn't have picked this out as a first game, which is always a good sign of things to come!