I don't think you (as a user) can adjust the sizing inside that element/panel.
As of now, you can only resize the lyrics if they're available as an element in their own panel. (either on the sidebars or left/right main panels)
You can try requesting an increase on the lyrics width in that "now playing bar" element or alternatively:
I noticed that the now playing bar also supports theatre modes.
So given that, you could try creating your own TM that resembles the now playing bar. (cover art, track info, lyrics and artist picture)
With a TM of your own, you would be able to decide where those 4 elements are positioned or how they're sized.
Edit: You can also try reducing the lyrics font size in preferences -> Layout(1). I believe a smaller size would fit some long lines into one line.