the music gets kinda fast in the end.

Wow, you lost 0.217 sec at the start and still got that time. so <4.5sec is possible! And for the background. You are right but I'm no artist. For the most part I googled the things I needed and tryed to recreate it :P (Check https://glimmer5r.itch.io/can-flip-3d to see my full artistic potential.)
The art is nice. The kind of control does not fit with the level design. The acceleration feels like the figure is stuck. I can't do exact jumps. Aswell as the breaks. Can't stop at the very edge. The controls tell me to go fast. The level design tells me to go precise. If you crips up the controls it's a great game. go on!