Apparent Centering Problem When Using the Perifocal System to Draw Orbital Ellipses
I solved the issue.
Everything I posted in the OP was correct; I made a simple, stupid sign error when transcribing the expressions into code.
It should also be noted that in the OP, the expression for Pk is wrong.  The correct expression is
Pk =   sin (inc) sin (aop)
Just in case anybody is trying to pull this off themselves!
Thanks for the ideas everyone!
Correct Orbits: