How many miles did you drive on the mixed fuel? If you did not HEAR your engine complaining (knocking / pinging) then it’s unlikely any mechanical damage was done…The only real problem would be if you tried full-throttle acceleration…You would certainly have heard the engine complain then…
Another unknown is the actual percentage of diesel fuel in the “blend” you purchased…How much diesel did the driver dump in the storage tank and how much gasoline was in in the tank when the fuel was delivered…
Hopefully, you can just drain your gas tank, refill with gasoline, and drive on, $600 to the good…