The thing is that you pay
- the reduced fine within 30 days (for speed cameras) or
- you pay the normal fine within 60 days or
- you pay the increased fine within 105 days
If you haven't paid within 105 days (it's 90 if you haven't been caught by a speed camera), the public prosecutor will try to get you to pay the fine either by means of an
ordonnance pénale or by taking you to trial. Either scenario seems unlikely to me if you don't reside within the European Union.
At best, they'll send the ordonnance and ask you to pay the increased fine. I doubt that they'll give you anything close to the maximum for a first timer. More likely seems that they'll keep the fine on file and if you were ever to be stopped by cops and they check for unpaid fines they'll see it and you'll have to pay on the spot. As an exception, you can risk a trial if you have numerous unpaid fines.