I put some clips together, which totaled almost exactly 30 minutes, but the exported file, when I went to check it, was an hour long, I need some help with very basic use, as iMovie has begun to fail horribly.
If you put the clips on the timeline then possibly there is a clip lying off to the right out of sight?
@Derek suggested a very likely possible reason. To be more precise, the real project/movie duration is reflected in the UI on the right side of the area shown below
The last two digits are frames. So, this example is almost 30 seconds long since it is 30 fps. Often media players show time as Hours:Minutes:Seconds. That might be another source of confusion about the duration.
Also, it may be possible that if you change the Frames/sec in Export you introduce a problem, but usually that is a small difference. You should avoid changing it there and change Video Mode instead.
It would help people to understand better your problem if in Shotcut you positioned the playhead at the end of your video and posted here a screenshot of the full Shotcut window. That way people don’t have to guess at what you are describing