iternabe The gain may sometimes be called sensitivity, or even just volume on the microphone setting screen of your chromebook. It will be just like a volume slider bar. Try increase it to see if your recording end up louder.
It sounds so stupid, but I never even thought to adjust the microphone setting on my chromebook previously - I had never made any sort of recording before or done a video call, so I didn't even realise there was a microphone volume setting! However, I successfully found the slider bar, and found it was on a very low setting so I turned it up to the higher setting - problem solved! 😄 This small thing made a big difference to my recent recital recording. Thanks for your help @iternabe .