I also played alone. I understand the gdevelop staff wanted people to make a lot of multiplayer games, but sadly it's not always convenient to play in a jam context 🙁
But even alone I had a lot of fun with your game! I like the concept a lot, it's simple and intuitive, and I really appreciate that you can play solo. The difficulty grows at a nice pace, too.
I used to play NES Super Mario Bros and Zelda with a friend on emulator with two controllers (me managing the arrows and him managing the action buttons) and we had a lot of fun. This reminded me of that, so I definitely see how this would be even more fun with 2 players!