Sorry I don't have 'Rescue...' here, but in other Magix video editing programs the simplest way would be to make a copy of your full project and then delete half the material from each. First half only on one copy and last half only (moved to the start) on the other.
Note also that there should be an option in the burning menu to adapt the bitrate of a project to fit the disc-- get a longer playing time but at lower quality. If you are just over one standard DVD length the reduction may not be noticable.