すみません、ここは女性専用車両でしたか？次の駅で降ります。 — Excuse me, was this the women-only car? I will get off at the next station. (Train · Subway, Formal — to staff, JLPT N4)

Gesture & etiquette

Slight bow, apologetic expression, and point towards the exit or next station.

Women-only cars are typically enforced during rush hour on specific lines. While usually not a major issue if you immediately recognize and correct your mistake, try to avoid them if you are male. Look for pink markings or signs on the platform and train car.