By design, the Gantt timeline in the Project menu > Plan > Schedule page is intended to give project managers an overview of the entirety of their project with a month added to the view at the start and end of the project - no matter the duration of the project.
For longer projects, use the scrollbar to see the end of the project.
You can extend your project past these dates by dragging or resizing the task/stage pills and refresh the page to see the changes.
Or, choose the stage that you expect to run the longest. Click on the pill and set the planned end date in the sidebar. On refresh, the view will resize to fit the new timeline.