This a nice game for a first Game Jam. I would have some suggestions: 

• First thing, I hitted a cloud that had hitbox outside of it. So maybe you could make hitboxes a little smaller. Even if they are all rectangles, if you just fit them in the clouds it would be more accepteble for the player when they hit a cloud.
• I noticed that sometimes when holding W I would fly up and then stop, but the duration was a bit random, so maybe you coud make it more like a flappy-bird such that you can't hold W but would have to press it repeatedly.
• Or instead of flappy-birding it you could add a fuel that would refill over time. Just a number on the bottom of the screen would be enough to tell player how much is left.
• And furthermore, instead of reffilng the fuel over time you could make some fuel pickups that would give player some fuel. This would also encourage player to make more dangerous feats.

Keep in mind that all above are just some suggestions, what you made is really nice especially considering this is your first Game Jam. Keep up the good work!