Weight is no way to judge whether you're fat or slim. Weight goes on in weird places and sometimes you genuinely can't tell. I speak from experience there, no one believes me when I say I've gained loads of weight recently.
Basically, body weight is distributed unevenly or evenly in different people, and as long as your shape looks OK to you, you have no health problems or severe fitness issues, and you were comfortable with yourself before the **** of all *****, the SCALE got involved, don't worry and from now on go on how you look, feel and how clothes fit, not on some numbers flashing up on a scale.