I was able to beat your game despite it not having an end, I understand this is a jam game and time gets the best of us but here are somethings that I would needed to be fixed or changed in your next version:
Enemy bullets shouldn't send the player flying into the air
Enemy bullets sometimes phase through a platform they are shooting at causing then to fly throughout the map
Enemy collider for the slingshot needs to be raised, instead of the bullet going through the center of the enemy it should hit the entire enemy to disable it shooting
Some platform structures have an edge you cant get over without jumping like your Z shaped platforms
When the player hits the side of a platform they freeze in place I am assuming this is because there is logic in place that says if the player is touching platform player vertical velocity = 0 which makes for some odd hanging options for the player.
Slingshot bullet size could use increasing
Win condition could easily be a a box collider where the stone is in the box we run a win function that changes the screen or does something.
Okay changes/fixes over.
This game is simple and once you kill a good amount of enemys is straightforward to beat for sure. For a first game/jam project I think you did well given how ever much time you gave yourself. Well done on posting a working game!