4 Bars per Line, Excluding Pickup

It's easier to help given an actual score, not just a picture. My guess is the music size is simply a little too big to allow another measure to fit, and you'll need to reduce it in Format / Page Settings. You could also try reducing stretch (select the measures you want narrower, press "{" as often as desired), but I suspect even if it allows the measures to fit, it will look too crowded.

Realistically, the four-measures-per-line convention isn't meant for music that complex - it's mostly used for lead sheets and children's books. Just going the with the default layout will usually look better than trying to force anything different in music like this.