mine shows this gap, too.
according to the service manual the replacement procedure takes untightening the torque screws and levelling the keyboard cover (!! only the cover where the gap appears !!) slightly up until it snaps off.

it is held by clips. i think those are getting lose from normal use / force.
replacement part is about 9,99 €. i'll keep it this way and wait till it gets worse before i'll try to replace it. but it's good to know that it's only the cover and not the whole keyboard