You Tube page is not showing full page only on left side.

Reset the browser zoom with Ctrl+0, then maximize the browser with Windows key+Up Arrow; these two actions address the most likely page-zoom or window-sizing causes.

1. Reset and maximize the YouTube page

1. Open YouTube.
2. Press Ctrl+0 to restore the page zoom to its default level.
3. Press F11 once if the browser appears to be in full-screen mode, then press it again to test full screen.
4. Press Windows key+Up Arrow to maximize the browser window.

In Microsoft Edge, Ctrl+0 resets page zoom and F11 switches full-screen mode on or off.^1^

If the entire browser window, including its address bar, occupies only the left quarter of the screen, Windows Snap is probably arranging the window. Go to Settings > System > Multitasking and temporarily turn Snap windows off, then maximize Edge again.^2^

2. Determine whether the problem is YouTube or the display

Open another website in the same browser:

• Only YouTube is affected: continue with the browser steps below.
• Every website is affected, but other Windows apps look normal: the browser is the likely scope.
• All apps use only part of the monitor: skip to the Windows display section.

Also test YouTube in another browser. If it displays normally there, the issue is specific to the original browser.

3. If only Edge or YouTube is affected

In Microsoft Edge:

1. Select Settings and more (…) > Settings > About Microsoft Edge.
2. Allow any available update to install, then restart Edge.
3. If the layout remains incorrect, select Settings and more (…) > History > Open history page > Delete browsing data.
4. Set Time range to All time.
5. Select Cached images and files, then choose Clear now.
6. Reopen YouTube and test it.

Microsoft documents cache clearing as a remedy for webpage display problems.^3^

If that does not work, repair Edge:

1. Close Edge.
2. Open Start > Settings > Apps > Installed apps.
3. Find Microsoft Edge, select its menu, and choose Modify.
4. Approve the prompt and select Repair.

An internet connection and administrator permission are required. Edge repair should not affect browser data or settings.^3^

4. If the whole Windows display is affected

1. Right-click the desktop and select Display settings.
2. If multiple screens appear, select the monitor showing the problem.
3. Under Scale & layout:
   • Set Scale to the option marked Recommended.
   • Set Display resolution to the option marked Recommended.
   • Set Display orientation to Landscape, unless the monitor is intentionally rotated.
4. If the resolution changed unexpectedly, go to Settings > Windows Update > Check for updates to obtain available graphics-driver updates.

A non-native resolution can make the display appear small, centered, bordered, or stretched.^4^

References

1. [Windows](https://support.microsoft.com/accessibility/edge/accessibility-features-in-microsoft-edge#make-text-larger)
2. How to fix auto split windows? - Microsoft Q&A
3. What to do if Microsoft Edge isn't working | Microsoft Support
4. [Windows 11](https://support.microsoft.com/windows/hardware/display-graphics/change-your-screen-resolution-and-layout-in-windows)