When you say that your web pages are small and narrow, I assume that you mean that the window isn't full size. If so, don't use the 'maximize' button to enlarge the window. Instead, place the mouse cursor over one edge of the window. When you see it change to a double-headed arrow, click the left mouse button. Keep it held down while dragging the edge of the window to meet the edge of the screen. Repeat for the other edges.
Windows 'remembers' the size of a window which has been dragged to size. (It doesn't 'remember' if you use the 'maximize' button). In future, your browser window should now open at full size. (Close your browser, and then re-open it, to check).
Chris