no way — Doubling, or even tripling CO2 concentration does not significantly affect the amount of oxygen in the atmosphere. Consider these facts:

Dry air from Earth’s atmosphere contains 78.08%nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and traces of hydrogen, helium, and other “noble” gases (by volume), but generally a variable amount of water vapor is also present, on average about 1% at sea level.

So you think decreasing oxygen from 20.95% to 20.90% or 20.85% is going to make a difference to your body?