If you are using the current version of Audacity the limiter has changed and you should be using 36Audiobook-Mastering-Macro.txt.
…Or, you can manually run Loudness Normalization set to -20dB RMS.
Then to push the peaks down into spec, run Effect → Legacy → Legacy Limiter with a limit of -3.5dB.
Note that by boosting by 8dB to hit the RMS target you’ll also be boosting the noise floor.