my SIms 4 game isn't going back to full screen

I don't know what happened but a couple days ago i noticed my Sims 4 game is not full screen, i can see my taskbar on my desktop and the top were the x is and the square to make it big or small. I tried refreshing my computer a couple times, then did a scan. i tried playing they was it is but i was getting distracted by the taskbar and the top of game to quit or make it big or small. i don't know if the update did it or i hit something or one of my guinea pigs i had out on my bed walked on my keyboard. I want to fix it to have full again were i can't see my taskbar on my computers desktop. can someone help me please