Disable system stretching to take up entire page width

I'm working on a piece where most systems only have 2-3 measures per system before I use a system break to force the start of a new system. The measures aren't particularly long, and if they were left to their default formatting then each system might only take up half the page width or less, which is what I want. But every system is getting stretched to take up the entire page width, causing all the notes to be spaced very far from each other, which I don't want. Is there any way to disable this automatic stretching, or to manually force the measures back to their default formatting? When I use the Stretch commands in the Format menu, nothing happens. I'm on version 4.5.1 on Mac if that matters. I appreciate any help.