Adding to an existing project

Audacity 2.3.3. Windows 10

Apologies in advance for being a newbie and an old man who is not nearly as tech saavy as my grown ass kid. I recorded audio using focusrite set-up and saved it as a project. I then opened up the project and added music to what I recorded The music is in stereo and the audio is mono. When I try to record more audio, the recording defaults to stereo and the newly recorded data appears on the music track. If I try to cut and past the new audio to the existing audio track I get an error that says I can not add sterero to mono. How can I get it so that when I hit record, the recorded material shows up in mono on the mono track rather than in stereo on the soundtrack track. Thank you.
Thank you.

you can always decide to add new Recordings in STEREO or MONO. Select this with the STEREO/MONO dropdown (here called “recording channels”)

If you select MONO the new part will be added to the mono track. If you select STEREO the new part will be added to the stereo track.

You also can reduce a stereo recording to mono:
Click on the steeo tracks name (here called “track menu”) in the TRACK CONTOL PANEL

In the dropdown select SPLIT STEREO TO MONO
At the end delete one of the both tracks

Thank you!