Well that was pretty cool of your girlfriend...obviously you will most likely not try to return it, as it was a gift. However, as the previous poster implied, if you get even halfway-serious about MTB, you will probably need a different ride. But for now, enjoy the hell out of it and have fun. The suggestion to take it to a bike shop and have it checked out/tuned-up is a good one - sometimes the assembly quality can be quite poor, which could result in potential serious injury for you...