Hey Dusan!
The answers here, while right, don't really help with your problem. I'm no expert, but I think I have a solution that could help you.
1) Export your track to a stereo wave after finding mix levels you like. Your volume levels can be nice n' low (-8 to -12 db is what I do). Then close your CWB file.
2) Open a new EMPTY project, add an AUDIO track and FILE > IMPORT your stereo wave file.
3) On the left you'll have your Pro Channel modules. I like to delete them all, except EQ (which you can't delete). Set your EQ to what pleases your ear by double clicking the "screen" on the EQ module (again, this is just an exercise in improving volume). I usually set a sharp slope (48) and freq to 24, but again, that's just me.
4) For ease of use, next add a Compression Module in your Pro Channel after (below) the EQ. (Add it with the plus icon at the top of your channel strip, still on the left of the screen)
I like the PC4k Style Bus. To start, you I like to tweak threshold and attack. Turn thresh all the way up (no compression) and gradually lower it about -2 more to cut off possible high clips. You can use the attack as well to tweak the tone. I set the release to 0.
5) Finally - the coup de grace - ADD (plus symbol) a final module > Style Dial Knobs > Max. This is a limiter and should come at the bottom, end of your chain in your channel. It's good for dummies like me because it's just one big knob. Find the loudest part of your wave and turn the knob until you are at 0 or even +3 DB on your channel. Make it loud, as long as it's not clipping. This is where your quieter recording pays off - if you record too loud, a limiter can make a throbbing, pulsing sound. Because you kept your levels open to headspace, that shouldn't be an issue!
This will be the volume you're looking for. Export to wav or MP3 and you'll have some color to your song, but also a "real recording" volume.
There's a zillion more nuances in these plugins but they are fun to figure out. The Style Dials seem to be made for amateurs like myself and so I put them in from time to time as the audio changes are very apparent. Many other plugins are much more subtle.
Hope this helps!
PS: Here are two examples I recording this morning to prove the point (not to show off anything in my writing or playing)
Before mastering: https://www.mountainouswords.com/wp-content/uploads/2022/03/Facing-Up-1.mp3
After: https://www.mountainouswords.com/wp-content/uploads/2022/03/final-boost-master.mp3