How do I get my desktop display back to normal size??

Suddenlly today the desktop info is too large for the screen. My dock located on the bottom disappears if the top toolbar is displayed and I can get it to show only by putting the arrow at the bottom, at which time the top of the screen with all the icons disappears. And vice versa. Also, all of the info on the dock (bottom) and top won't fit laterally, e.g., to get the Trash to show I must slide the arrow so that the Finder and Launchpad on the left end disappear on the left.

How do I get the desktop to fit the screen again with all the icons and info lists appearing simultneously as always before? Thanks!