Keep the tank brimmed with diesel for a few days to reduce the % of petrol in the tank
9/10 out of 10 you'll be fine
Bloke I bought my MK4 off stuck £40 of petrol in it, it cut out on him, syphoned it out, brimmed it back with diesel and the engine was fine. Did over 60K since it happened
Also change the fuel filter towards the end of this week