Skin in cleavage is lifted "tenting"
Thank you for your question and photographs and I am sorry that your current results have not been what you anticipated. Though nothing replaces an in-person examination it appears that you have a separation between your breasts and it is unlikely that you have synmastia taking place. I know that waiting is difficult but allow your results at least three more months to mature to see if the tented skin resolves. If it does not then a more narrow implant is likely needed to help minimize this appearance.
You do have defined cleavage plane and do not look like you have symmastia. You have some tenting which may improve with some more time.
In the absence of synmastia which cannot be always diagnosed from a photo, the only way to correct her cleavage and not have tension placed on it is to have a less wide and less towards higher profile breast implant. From your photographs preoperatively, what I see postoperatively is a magnification of cleavage that is very close. You might want to consider a smaller, less wide and flatter breast implant. Good luck.