Happened to me too early in my C172 career, and I agree with the other comments to the effect that the aircraft was still flying (i.e. you "landed" much too fast".
One of the most eye-opening experiences in a C172 was practising really slow flight (with an instructor) and full stalls (not just approach to stall until the horn starts sounding). It's amazing at how slow speeds this thing still flies, and it'll give you the confidence you may need to fly the approach at the correct speed (which may seem much too slow for your own liking).