wrong dimensions, please help

hi! just put online my first page https://www.djpakalpojumi.lv
designed using twenty-eleven child theme
and got my first dose of noob mistakes ??
it is displayed ok on my laptop but on bigger monitors there is wrong dimensions, resolutiom,right corner disapears, everything seems too big

can somebody take a look? what can i fix?
please, please, help!!! i need to fix it asap