I am sorry for your concern. I would recommend d/w your plastic surgeon. From the story and picture provided, I am not sure what is going on. Perhaps he/she was worried about blood supply to the nipple and wanted to use the fewest sutures possible so that blood supply wasn't further compromised?
Not sure what is going on here but your surgeon would know and should certainly be able to guide you. He/she will know how much deeper tissue support (with sutures) are in place and when the external nylon sutures should be removed. Likely will heal better than it looks now (acute swelling is making it look worse), and one approach is to let that happen and if an objectionable scar later, revise that months later. I would recommend antibiotic ointment (at minimum) for any gaps like this in the meantime, but if your surgeon is willing to put in more sutures at this early point, even better. The most important thing is that the nipple looks fully healthy blood-supply-wise, which greatly increases your chances at adequate healing.