Try these checks in order:
- Open Start > Settings > System > Display.
- Confirm Display resolution is set to the Recommended value.
- Under Scale, set it to 100% or the recommended value.
- Open Advanced display and choose the highest available Refresh rate.
- If more than one display is connected, select the correct monitor in Display settings.
- If the screen is still stretched, open the monitor’s built-in on-screen menu using its physical buttons and reset the monitor’s aspect ratio, size, or Auto/Screen Fit setting.
If the issue started after connecting an external monitor, a temporary resolution change can fix incorrect fitting:
- Go to Start > Settings > System > Display.
- Select the external display.
- In Display resolution, choose a different resolution than the current one.
- When asked “Keep these display settings?”, select Revert.
If the display is flickering or looks corrupted along with being stretched, reset the graphics driver by pressing Windows logo key + Ctrl + Shift + B.