I really enjoyed this, it's very good for a first time pico-8 dev. I especially like your pixel art, it looks really good here.
The gameplay is fun, though it is a bit awkward just how precise the hitboxes are with shooting your fireballs, even just one pixel too far off and when you think you should be hitting you end up missing.
I think the first stage feels a little too empty at times too, i get that you don't want to overwhelm the player with too many enemies early on, but there was still a bit too much downtime between enemy waves, so perhaps you could find a way to make the enemies spawn differently to keep the pace of the game going.
Good job on the music, that's something I always struggle with in this engine, my brain just doesn't work that way, but you managed to make something that has a good tune and is pleasant to listen to through the whole game.
I look forward to following your work and seeing what else you make in pico-8. Welcome to the community!