Wrong fuel

If you have not run it yet, you will need to use an extractor pump and remove as much of the diesel as possible (all of the mix in the tank would be good). Then fill the tank with clean gas. That will dilute the diesel enough that it will run. Then just keep using gasoline.

If you did not catch it before diesel went through the system, you will need to do the pump out as above, then disconnect the fuel line under the hood and pump the gas through the lines to flush the diesel out. Once that is done you should be okay.