How do I save a video with voice over?

The question seems pretty simple, and I’ll admit, I’m a complete novice to editing and I’m probably either taking on a project that’s too complex or I missed a step somewhere…

I got my video completed. I added my voice over. In Shotcut, it works perfectly. Then I went to export the entire file - I’ve now done it twice (about 40 minutes each time for a 5 minute video without a lot of extra filters, just the voice over and a watermark that is already embedded into the video…)

I tried to export it from the timeline and it failed, so I tried to export it from the playlist . When that didn’t work I tried to download each item in the playlist, and that didn’t work either.

These are my export presets:

video_off=1
f=mp4
acodec=aac
ar=48000
ab=384k
vcodec=libx264
vb=20M
g=15
bf=2
width=1920
height=1080
aspect=1.77778
progressive=1
top_field_first=2
deinterlace_method=yadif
rescale=bicubic
r=30
threads=0

Am I missing something? Thanks!

Johane