You could have accidentally put an exposure compensation or a flash exposure compensation. Here is how exposure compensation gets set -- https/support-in.canon-asia.com/contents/IN/EN/8202786400.html
Here is how to change flash compensation -- https/www.dummies.com/photography/cameras/canon-camera/adjusting-flash-power-with-flash-exposure-compensation-on-a-canon-eos-70d/
You could have accidentally put an exposure compensation or a flash exposure compensation. Here is how exposure compensation gets set -- https/support-in.canon-asia.com/contents/IN/EN/8202786400.html
Here is how to change flash compensation -- https/www.dummies.com/photography/cameras/canon-camera/adjusting-flash-power-with-flash-exposure-compensation-on-a-canon-eos-70d/