I don't think there is. This is really weird that your car is locked as they shouldn't lock themselves!!
Not sure about the coupe but I don't know how to open the boot from inside the roadster.
On the roadster it's in the glovebox behind a plastic cover - the handbook shows this being removed using a key
lots of factors affect the result - heat soak, time since last service, octane rating of the fuel you use was the figure quoted at the flywheel or road wheels?