So my Audi A4 B5 Avant has just had 15.00 worth of super unleaded petrol put in it, the problem is, it is diesel. The needle was nearly in the red when I filled up. I only drove the mile and a half back to my home, but what type of damage will this do? does it need to be syphoned out?

My mum as a petrol and I fill her car so got muddle for once.