Actually, I tried using the whole available canvas (the first few progress images in the thread use it), but it wasn't working out after I made the boss sprite (I made the cards first and the rest of the GUI semi-last) and I've had problems with choosing a good composition so I had to shrink it  Not sure what could have I done to reduce the GUI to give the boss visual priority while maintaining readability at the same time.

What jal says =)

Layout is a bit cramped. You should have used the whole available canvas, and / or reduced the GUI items to give the boss visual priority.

Very nice from you.
You are getting much cleaner and sharper