I didn't get why the player sometimes jumps higher or not. Thought it is connected to the (annyoing) white beating bar at the top...but it did not fit. I think this one is the part that also fits the theme, however, refinement definitely is needed here. The Window size is also a bit of, but this is often a common problem of Godot. Here you need to check screen sizes, project settings etc.
Still: Congrats on creating a game within this short amount of time, keep going!