Sims 4 opens really small

Something is really wrong .... I just bought and downloaded Sims 4 Deluxe.

After installing, the game opens really very small, about a 4 inch square in the middle of the screen surrounded by black. I cannot click on any buttons in the actual game screen (mouse will show up as a magnifying glass when I hoover over the 4 inch square) ... I can ONLY work the buttons if I click 'somewhere' in the balck part ... ?!

is there a way to make it full screen  (I have a retina screen). Do I have to adjust some settings somewhere on my macbook? 

It is impossible to adjust anything in the actual game mode/screen since I have to click 'somewhere' in the black to get there i .... 

The game is worth nothing like this. Totally unable to play.

Many thanks for your help!

Jeannette