I mistakenly put diesel in gas car and drove it 3 miles . So how does it damaged my car
A diesel fuel pump nozzle won’t fit in you fuel filler opening. Just curious how you got it in there. The compression of a gas engine is not high enough to ignite the diesel fuel. At the very least your gas than will have to be drained and the fuel ines blown out with air.
I presume that this diesel fuel was in a gas can…not at the pump, which as @oldtimer-11 mentioned…they wont fit.
How much diesel was added. If it was a small amount 1-2 gallons you may be able to dilute it with a full tank of high grade gas. You would still have to flush the fuel lines though before trying to start it.
Although the misfiring was likely quite noticeable, which could adversely affect the cat among other things, probably no permanent damage. Ask a shop to drain the tank, then re-fill with fresh gasoline. If it runs the same as before by the second re-fill, you’ve got it licked. If not, post back and you’ll get some ideas where to look next.