Anyone know why my grid is no longer filling up the space of the section?

Maybe it's been like this all along but I don't ever remember the grid not taking up the full space of the section.  I can actually put a text box or video or image over to the white space where the blue line is but I always thought it took up the whole screen.  Is this new or am I just being old and forgetful? Is this some sort of margin i have set and don't realize it?