You have done well to get that many flowers! Jack O'Lantern grows basket ball sized fruits, even if half of those are fertilized you will still have a large crop. I would wait and see how many are fertilised and subsequently start to develop, plants are usually quite good at limiting themselves to what they can support. You may find only a small number actually get that far. If they all start to develop then I would thin some out! ;D
I haven't even planted mine out yet.... :-\