So basically the aircraft was over gross weight before you put any gas in it
Well, looking at this example
Weight & Balance Calculator Cessna 152 - Javascript This gives a useful load of 520lbs, 2x 14.5 stone =406lbs, so not over gross! In fact this leaves 114 lbs for fuel ~ 18USG, not full tanks, but certainly more than enough for a couple of hours plus and shows it can be done, I know there will be some with a higher DOW, but even these should be workable with care - but it still does not mean it will be a roomy learning environment!