the widest implants for the volume you want must be used. Now that you're post-op, would you like to go larger or not? If so, a larger, wider implant would help but your nipples may lateralize a little as the majority of the implant will be medial to it. If you don't want new implants, you can, as suggested by the others, have fat grafting to the medial poles to diminish the space.
If you have a large space between your breasts, a breast augmentation will not necessarily narrow that space. Cleavage is not something that implants can create, however, a fat transfer to that area can make some very nice improvements. Discuss this with your plastic surgeon in person to determine if you are a good candidate for this procedure.
Some women naturally have a wide gap between their breasts which may not change after surgery. If the implants were placed behind the muscle, the gap will probably remain the same. Sometimes fat transfers can improve that area, but you must have fat available to transfer. I would suggest discussing your concerns with your surgeon.