Thank you for your feedback.
The levels are a bit hard actually but if you understand the rewind mechanic correctly you can pass the levels.
Your echo is showing you the place that you have been 4 seconds ago. If you "hold down" E it starts to rewinding. You can release the E whenever you want.
To be honest I suck at background music. So if the player listens the music too much he/she can be disturbed because of it I decided to put the music only in menu.