Well, most two-seat light aircraft don't have enough payload to carry full fuel and two average male (by 2011 standards). The way I see it, you have 3 choices:
a) fly with less-than-full fuel, which means you have to refuel after every lesson or even make a fuel stop during cross-country flight
b) find a different instructor-student combination that will allow you to takeoff with full tanks
c) accept all the risks involving the over-weight aircraft (but do make sure the CG is within limits) and fly the aircraft accordingly