Great first effort;
Feedback: (just my opinion)
Be consistent in art style; pixel art is ok. I am sure you will develop it better as you do more, but the background is not pixel art. I would replace it with pixel art or gradient shade.
The sound is nice, but the timing is off. Also, the music does not really kick in for a few seconds, So I would suggest that during that time, you wait before spawning the clouds and rocks.
Currently, the side clouds move too fast for you to use the side area effectively, thus reducing the game area. Also, nothing else appears to come up from the bottom, so the most effective strategy is to move to the bottom to avoid falling rocks.
Build yourself bits of game/code elements that can be posted into future jams. For example, when you build a high score for one game, make it so that you can easily slot it in for another.
Great effort