Overestimating the extent to which others notice and evaluate our appearance and performance is called

The answer is: the spotlight effect.

People who experience a spotlight effect would perceive that they are receiving more attention from other people than they actually do.

This effect tend to be caused by irrational fear of social judgement. The fear caused personal insecurities that make the victim felt every gesture made by other people was made to mock him/her from behind.

Example of a spotlight effect is when an overweight person felt insecure about their body and falsely perceive other people who are having personal conversation behind him are currently mocking his body.