Volume sounds good in Audacity, but resulting MP3 too low

I’m a total audio noob but I figured out how to record sound from my PC (me playing some games). The recording inside Audacity sounds good and loud enough. When I save it, however, the result is an MP3 that is way too quiet. Any advice? Maybe a setting I’m missing?

Import the MP3 back into Audacity. Is it quieter (less tall waves) than the project?

If so, check that you did not knock the -…+ gain slider on the track when you exported.