It's far better left to ripen on the plant, though you can eat them unripe, rather like courgettes. At this stage in the season, I'd count my chickens and let one big one ripen rather than gamble on the smaller ones growing larger and ripening in time.
I've the same problem with several butternut plants, and in future, it's best to remove the first fruit which form when very small, and wait for several female flowers to be open and be pollinated at the same time. You do this with melons, and pinching out the main leader on the squash would encourage flowers and fruit to form on the sideshoots.