Cool entry, it's very difficult :D
Here's some feedback:
- Key to game music is that it (most of the time) should be in the background and not too attention grabbing. Focus instead of adding a few sound effects, this will give your game a lot of "game-feel" for very little effort.
- Same goes for adding simple 2 frame animations, or in this case simply rotate the sign over half a second or so when you swap direction instead of snapping it 180 degrees.
- A simple score would add a lot of replay value, just check the distance that the player has traveled in the X-axis from the start position and display that on the screen.
- You have a good base to work on, adding small things like screen shake and particle effects will go a long way to improve it.
Great job on your first game jam! :)