Hello everyone. Hope all is well.

So I'm about to finish and send my mixing to mastering engineer.
I want to clear all of their sonical requirements such as headroom etc.

I checked my Peak and RMS on Ableton. and loudest Peak was around -3db and RMS -9db.

I have few questions:

1--Once I bounced it, the peak gets louder like almost hit 0db. How can I keep bounced audio as I checked before bouncing? will real time bouncing help or there another way?
2--Mastering engineer ask me to check Peak/RMS ratio and usually if the peak is -3db RMS should be -13 to -17db. But mine is much narrower. Does that mean the way I mix isn't ideal for mastering? Or I should check meter in right way??
3--So after all, what's the best meter plugin for checking if my mixing is
ready for sending to mastering engineer? I want simple one as possible but of course willing to learn how to use meters. So far I have quite many Waves plugins, I bought bundle. I think I should have enough but not sure..

I'll appreciate you guys's inputs!!!

Best regard.