Thats roughly 25% mix of petrol, that's a bit on the high side.

How far have you driven it since?

My son did exactly the same with his Mazda 6 - he put £20 worth of petrol in an empty tank. However he followed my advice and filled it to the brim with diesel. I told him to top it up at EVERY occasion and after a few fill ups it was fine. That was 3 years ago and the engine runs fine. If you'd have filled it with 75% petrol then you would have needed to drain the tank. 25% is just about ok - it'll be a bit clattery but as long as you don't thrash it it should be fine - and that's from someone who's been working on diesels for 40 years.

Hope this helps

Robin the Technician