Dealer undercharged

[XlR8TED]

So I picked up my new Focus XR5 on Monday afternoon and upon getting home noticed that the figures didn't seem to stack up. I had a trade + a deposit & financed the rest. However, the total of these figures did not total the purchase price of the car. Infact, it was a few thousand less.

I've just received a call from the dealer asking me to come in to re-sign some forms as 'there was some incorrect details on the original document'. Obviously they've picked it up.

I know the moral thing to do here is to re-sign and have the loan amount reflect the actual change over price, but I would think having a signed legal contract with the lower amount would allow me to tell them to bugger off. In short, I've got them by the short and curlys, no?

I will end up doing the right thing, but I think I might make them sweat it a bit.

What would you guys do?