To configure the render according to your needs and to obtain the desired output, you will need to check on what your settings are for these three items:
Rendering takes a section of the timeline, performs all the editing, effects and compositing, and creates a new media file. You can then delete all the source assets, play the rendered file, or bring it back into CINELERRA-GG for more editing. All rendering operations are based on a region of the timeline to be rendered. You need to define this region on the timeline. The rendering functions define the region based on a set of rules. When a region is highlighted or in/out points are set, the affected region is rendered. When no region is highlighted, everything after the insertion point is rendered. By positioning the insertion point at the beginning of a track and unsetting all in/out points, the entire track is rendered. But you also have the choice to render one frame. Reminder, CINELERRA-GG does not do remuxing without rendering - see Transcode.