I am working on a 20sec intro clip and the program insists on the video to be 2min long with tons of empty space at the end... How do I "end" the timeline and cut the last 1min40sec?
You most likely have something somewhere on a track that is taking you beyond what you want. Expand the timeline window to full screen, press on f. This will put the complete timeline. Press End. Does the playback marker go to 20s or 2minutes?
Scroll down vertically to see if there is not something on a higher numbered track somewhere. Sometimes it's just a fragment.
If worse comes to worse, select all objects on the timeline up to the end - the 20s mark - copy, open a new movie, paste. Try exporting this movie.
Alternatively, set a range for what should be the start and end of your project, and export - click on export range only in the dialogue box.
One last thing, make sure that you don't have a range set longer than the end of the project and are exporting the range.