If it is more than just that one webpage. There are several methods to get the webpage to open full size.
Right click on explorer properties and then open maximum. It must be set this way
Then
When it does not open full size, stretch it to full size, hit the full size square on upper right and then close by hitting file and then the exit.
and/or
While its full size hold down control and then close the page.
and/or
Hold down the Shift key while clicking
"File, Close". Always open IE 8 in a size of your choice. - Windows 7 Forums
Why so many suggestions?
The reason is that this question is as old as the hills. Takes a while for Windows to remember dozens of attempts, sometimes. Finally you may want to try the freeware that I have given in my link above.