To me, the font for "Bitcoin address" is hideous. It looks like you wanted to go for something "classy" and it shows. It looks Russian or Greek, not particularly "global" or "cyber" or "digital".
They are mathematical symbols, which are typically based on Greek Characters.
That back of the note is a wasteland. How could you design a note and leave all that real estate barren? You could put anything there - anything inspirational you like - and it's left essentially blank.
Some times less is more. I know most currency notes have a full design on both sides but I'm going for more of a playing card look.
Many of those notes are just plain ugly, I have a collection of nice notes that I used for inspiration.
P.S. Don't forget the rule of thirds. And *blend* the QR codes and numbers into the design.
The QR codes do have some slight transparency in order to blend them into the note, but if I messed with them any more they might become unreadable.