Is plica fimbriata always symmetrical? i have a noticeable flap (maybe 2mm) on one side, and only much smaller ones on the other.

Not always symmetric: Plica fimbriata are not always symmetrical. Best wishes.

Not always: The plica fimbriata is a slight fold of the mucous membrane on the underside of the tongue which runs laterally on either side of the lingual frenulum. The free edge of the plica fimbriata occasionally exhibits a series of fringe-like processes. They can become irritated during brushing or hygiene. Talk to your dentist.