Hi Libby
A curious question which I feel needs more detail from you. How did petrol get in the oil? Did you pour the petrol into the oil filler or is it some kind of mechanical failure that's caused this?
If you did pour fuel in the oil filler, you will immediatly have to drain all the oil from the engine and change the oil filter. Refill with fresh oil, run the engine for a few minutes and then repeat the process, drain oil and refill again with more fresh oil.
Rupert, April 2020