Justify margins - too many notes in the system

After setting the left and right margins, the score looks dreadful: In the right margin, some notes are suspended in midair.

capella indicates, that there are too many notes within the system. Re-distribute the notes amongst all systems (i.e. with menu extras | score wrap around) or select format | score | note spacing and tick "allow extra compression". In this case notes will be forced to fit into the system, possibly to the point of illegibility.