Your problem sounds a little tough, because the nipple seems stuck to the underlying pectoralis muscle, which means it gets worse when you stretch that muscle, like lifting your arm. What needs to be done depends on whether you had too much tissue removed or not.
If there no contour deformity (divot) when you are lying on your back, then the problem not overresection - the problem is that the areola stuck to the underlying pectoralis fascia. In this case, the scar between the areola and the muscle needs to be released and you need to move a lot afterwards and massage the area in order to maintain the release.
If there is a divot there, then you will need fat grafting, where fat is taken from another part of your body in a process like liposuction and placed in tiny droplets in to the divoted area. This will separate the nipple for the muscle for you.
Both surgeries are relatively small.
