Nice job! Really great especially for your first gamejam. The movement is fluid and I love the little music transition when you collect the heart. My final time was quite slow, 1:22!
I found it a little tough due to how fast the player moves and how obstacles are often hidden offscreen, meaning it's easy to run into a fireball without having enough time to react to it if you're running very fast. One possible solution to this would be to shift the camera forwards based on the player's current velocity, so if you're moving quickly towards the right, the camera biases to the right so you can see more of what's coming.
I like the ideas here, the speed of the platforming reminds me a little of super meat boy. There's also some really nice player-friendly design here, like the arrow showing where you are off-screen when you go too high.
Great work!