Mouse not staying in the game

I took a short break from the game. A friend of mine asked me to log on to see if it would be possible to get to the top of his base since I’m a ninja and always find a way. When I logged in everything seemed fine but I kept getting alt tabbed. Than I noticed the game isn’t keeping my mouse in game. It goes to my second monitor and when I click it minimizes the game. I though oh well I’ll just go full screen problem solved. Nope I was wrong it still goes out of the game. Is there anyway I can fix this problem? I browsed the first couple pages of the forums didn’t see any similar topics, but is anyone else experiencing this same issue?

HALP

i dont know if that helps with your case but try this:

hit F1 ingame

and type:
cursor.lock True