the agreement wont say anything about you not being able to afford the payments, it will say something to the effect of ' your right to terminate agreement,'
this is what it says on an old agreemnt we had :
termination--your rights;
you have the right to end this agreement. if you wish to do so, you should inform the person authorised to recieve your payments. ******** will then be entitled to the return of the goods and to half the total amount payment under this agreement, that is �********. if you have already paid at least this amount plus any overdue installments you will not have to pay any more, provided you have taken reasonable care of the goods.
so in other words, say your finance total is 10,000 and you have paid 5000, then you can give back car, end of story. if you have not paid at least half then you will be liable for the remainder of the full balance. hope you follow all that !