I've never made an over-sized block for a quilt back, but I really like the effect. The tiny one was an after thought as I was putting some scraps away.
I used some black polka dots left over from the shark quilt:
This black print is from Amanda:
And I had just enough scraps from the pink star quilt to make two of these blocks:
I decided to use the bright white fabric to make these two blocks stand out a little more.
New items purchased to complete this quilt: one spool of blue thread