Good entry for a first time Game Jammer! The Controls work fairly well, as well as all the other game mechanics. The pixel art is also looking great - you say, you downloaded fonts and audio, so I expect you created the game art yourself?
Some feedback for improvements:
- The colliders behave strange, when the character is on its upwards phase (it sticks to platforms)
- Having more than 1 live would be great
- The character not flipping when moving backwards irritated me more than once
- The height of the jump felt to big
Keep up your webdev journey, this is a great start!