I think the Regs are pretty clear.
A 2 hour flight that consists of a leg which is 100nm minimum in length.
Most people would fly 100nm from ORIG to destination as the first leg. Of course depending on where you located this could be difficult.
There is no mention that the 100nm leg has to originate from departure airport.
If the examiner proves this to be wrong, and the school knew of this, then the school should reimburse you of some sort. And I think a quiet word with your instructor as to why he's trying to pull a fast one on you to build hours.
I had a similar situation during my training where I needed to do another night X-country. I did no pay for it.