The simple and rather obvious solution to this is to let the tank cool down, and then top up the missing bar or psi. If you've done your math right you ought to be pretty spot on.
My club has a continuous blender, but I still top up. If not, I'd have some seriously short fills even when "overfilling" by some 10%. I don't bother with the mixer when I'm topping up, so I aim for 33% in the hot tank. That usually brings me within half a percentage point from 32 after topping up.
Now, PP blending into 300 bar tanks, or anything involving more than homeopathic amounts of He brings with it a whole 'nother can of worms called non-ideality or compressibility. Good luck getting close to the target if you use ideal gas behavior for those calcs