Can't sign in to pc

I needed to change the font in systems that went to 100 somehow and made everything too small. I changed font to 300 and now I can't sign in password bc font is so large the password box doesn't show up. Can someone help? 

I tried ctrl I, Windows-. Neither worked. Hope there's an easy workaround bc I'm not that tech savvy and my friends who are geniuses couldn't figure it out.