Suzuki: suski vitara 1.6 misfire on starting, colorado rocky mountains, gas car

Question
QUESTION: Filled up with what I thought was petrol last wed. Have done around 34 miles. Car smells of petrol and misfires when idling or starting up.Cannot get into a garage until next wed. Is it possible I put in diesel in error? Plugs have been checked and they are ok. Nothing obvious is wrong. A friend who was a mechanic checked a few things out and could only see a small amount of coolant leaking from the thermostat housing gasket. Is it safe to continue to drive? Can you suggest what it could be? Battery ok. It just judders until I get up to some speed. Thank you. Regards claire

ANSWER: If you put in diesel, it will start a little harder cold, not necessarily run smoothly cold, and possibly smoke a little when cold.  
The only thing I can imagine is that lots of cold short trips might be bad for the converter (cat)
Does this all clear up after it comes to operating temp?  If so, I wouldn't be very concerned
scotty

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QUESTION: Thank you Scotty. I only do short trips, never more than a few miles at a time. It does seem to clear and get better when I speed up a bit. Does this mean it is likely I have put diesel in and is it going to be very expensive to put right? I drove it yesterday and it was definitely not good but I did think that maybe it would have reacted badly at the time of putting in the fuel. I had a around a quarter of a tank of petrol in it before refueling. Someone has told me that the nozzle will not fit if it is the wrong fuel. Is this true? Thank you for your help.

Answer
I read that you mentioned it as "petrol", and was not certain that the diesel and no-lead nozzles were in fact different sizes where you live.  I'm in the Colorado Rocky Mountains, and it would be virtually impossible to fuel a gas car with diesel, but not at all difficult to do the opposite.
I would drive out another tank of fuel before making any judgements, unless it starts to run much worse quickly.  You could try adding a fuel additive, on the assumption that the fuel you got was less than top drawer.  Also consider whether you are having unseasonable weather.  That could have an effect.  

If it misfires on start up, does it clear after revving the engine a couple of times?  Does driving a gear lower than usual, at higher rpm have any immediate effects?