Thank you Pih!
I hope the game can help people to memorize the piano keys. I usually create games for music education so I had that in mind for this one too.
As for the keys guide on the right, unless I misunderstand what you are referring to, "it's not a bug... it's a feature" ;) Since the keys between "l" and "enter" aren't mappable in GDevelop, I had to end the keyboard input at high C. I could have gone up to high D with the letter "l", but I thought it would be less elegant.
Cheers!