They have a nice size already. sometimes they will abort and put their energy into other fruits. This happens more so to very young fruits from what I've seen. thinning is done sometimes so the plant may put more energy into the other fruits,, from what I've observed this may be of value for certain varieties as the carpels develop more and the flavor even may be sweeter / richer from the bigger fruits. I've had some great ~ 5-10 pound jackfruits etc but the best tasting ones have always been the ~30lb fruits where the flavor is really developed. since its still young I would just let it do its thing and you will see for itself. If it fruits at several different times then that is a bonus ! Enjoy