Lovely you noticed the details :) I could not resist to put the propeller from Flappy plane. There is some kind of bug when godot export the game to HTML and the speed bar does not show (it works in the windows executable). Every time you press right you increase the speed (constant press only changes speed to 1). If you press left, it decreases, and there is where you get the reverse gear. In the windows executable the bar will be blue for "forward" and yellow for reverse.
I will do a commercial version of the game in a near future, if you want to be a beta tester and give some feedback I would love to share a copy with you. Just let me know!