Is it possible to make a ISO of the main movie alone?

also just an additional question.. If any of you use FairUse, i chose to make the movie 700MB(which is max as i understand for the lite version) but the final movie came out to be a little less than 400MB, with nice quality. Does anyone have an idea of why it came out like this?
I would like for it to come out close to 700MB so i would get a little better quality.
Helps appreciated.