There is a permanent frame in the workspace in order to allow screen operations when the model is larger than the screen (rotate camera, pan etc). It is not possible to edit the model in this frame, only camera operations.
Is there any way to deactivate or resize this frame?
nope.
The border appears when the document is over a certain size in relation to your screen. You may find that by pressing TAB to hide the shelves, and possibly also pressing the Menus switch (top right of interface) to hide the menu titles, you gain enough space to stop the border appearing. This will also maximize the amount of workspace you have available and you can quickly get the shelves back by pressing TAB again.