Mesures

Put more music in them. Measures expand to accommodate their contents. You can also try adding system breaks to force fewer measures per system. They will expand to fit between the margins or you can make everything bigger by increasing the scaling Format>Page settings. It is best to let Musescore handle everything until you have entered all the music and then apply subtle tweaks to adjust things more to your taste.

If you give more detail about what you are trying to do, someone can give more specific advice.

See the Handbook section about Formatting:
https://musescore.org/en/handbook/4/formatting