Having a decent sized monitor definitely helps to see as much of the screenshare as possible. You can first make sure that your browser window is taking up the whole screen, and then you can also adjust the size of the windows within the chat room platform by clicking this button (just click the button again or hit the Esc key to go back to normal view):

And you can also maximize the screen share window and minimize the chat and attendee windows by clicking these arrows:

...or by dragging the dotted line that appears near the border of the window: