From my experience of training on 150/152 it is hard to load them outside their C of G limits, but easy to overload them.
You may find you are very close to max weight and have to reduce fuel load.
Note it is weight not mass as mentioned mass would be the wrong unit of measurement.
Good numbers to remember on fuel are 189lt=50 us gallons = 40 imperial gallons = 300lbs
It is important to learn how to do the calculation as you move on to more complex aircraft with multi tanks as the C of G can move as fuel is burnt on some aircraft, to the point that it is impossible to raise the nose on landing or it goes backwards with loss of pitch stability.
So I think the advice given is critical, not difficult maths bit of addition & multiplication. Best luck with test.