This was really good! The controls feel very natural and smooth, the graphics look great, and it feels very solid programming-wise. I feel like there are a few things that could be improved, though.
When I first found the boomerang, I had no idea what it was, the icon doesn't really resemble a boomerang at first glance. A little text prompt saying something like "You got the boomerang!" would go a long way towards making the game easier to understand.
Also, while walking left/right feels good, the jumps seem a little bit floaty.
Still, it's a great entry to the jam, and a great start for a full game if you decide to keep working on it.