PCP - Is this the right way to use this overpayment calculator on MSE

IAMIAM

£22600, 9% APR, 4 Years, £390 Payment, £9688 GMFV

Zopa allow overpayments, anytime, and recalculate monthly every time, and I have checked, if I continued, at some point, it eats into the GMFV.

https://www.moneysavingexpert.com/mortgages/mortgage-overpayment-calculator/

When I have inputed the figures and just kept a £250 overpayment ongoing from the start (this will have to increase to keep total payments monthly at £650ish) It calculates I will have paid £391+£250 every month for 2.5 years and paid a total of £3k interest and paid off the whole PCP.

Is this correct, as I am happy with £1k per year in interest for the car for 3 years.

I understand this is not the cheapest way to purchase the car and want to understand if what I am saying above is accurate, not to get a cheap bank loan, save cash, get a cheap mortgage, or get a cheaper car. Thanks.