They are trying to scare you for good reason…the bikes you will be riding in your course are in the neighborhood of 20-25Hp, the GSX-R is somewhere near 115-120Hp…that’s not just a step you are taking…anything over 75-80Hp is a pretty fast bike, so you can see where their caution comes from. If you cannot afford the Buell, or a similar powered bike, the rocket ship you bought really doesn’t “take off” until 7000ish RPM, so short shift…don’t allow yourself to rev it out…but that is only if you can’t find something else to build you skills on first. Of course this doesn’t take into account the very strong brakes, and responsive (read twitchy to a newbie) handling. Like someone said, these are basically racebikes that they put lights on…Just be very careful…my neighbor has a GSXR750, and that thing is a monster that really doesn’t like speeds under 50mph…
Good Luck.