Or the longer form of this reply, if you’re not real familiar with the program yet, is select your composition, then under the Composition tab at the top, go to Composition Settings, and make the Duration the same length or longer than the footage you want to edit. You can also set the composition length when you hit New Composition, but you don’t have to redo everything if you’ve already applied your effects. If your composition length IS long enough and it’s just only outputting a short piece of it when you hit Make Movie, then you can adjust it in your Render Queue before you hit Render by clicking on the hyperlink next to render settings after the dropdown. Change the timespan dropdown to “Comp length” or hit the Set button and set it however you’d like it.