Contrary to the X in the upper right corner used to Maximize the display the Full Screen is reached by pressing the F11 key. Or on Notebooks it may be a combination of Fn plus F11, different brands don't always do the same, may or may not use the Fn key but check the colored markings, if Fn is needed what the Fx key can do will be marked in the same color.
That said, does using Full Screen also show the individual slides at the bottom?