Diesel fuel in a gasoline engine

Unfortunately a diesel nozzle fits just fine in a gasoline filler neck. :( I only drove the car from the pump to a parking space, then called a tow truck. I had a really bad day that is lingering... I don't want to be taken, or lied to, to put it politely. I was told by the service technician (who sounded like a used car salesman) they only need to remove the gas tank. But, removing this particular year and model gas tank was exceptionally difficult because there are many big parts they have to remove (again on this year/model) to get to the tank and they need to remove the tank to drain it. The quote is $1200.
Thank you in advance for your help!