My screen is large and nothing will work to fix it

Hello,
My screen on my computer is extra large and theres nothing I can do to fix it. I cant even get into safe mode because i can't see anything because of the size. I tried to press ctrl 0, I've tried an anti-virus thing but its still too big for me to see anything to run it, and I tried pressing the f8 key to get into safe mode but that hasnt done anything either. I really need help.
-Emma