How long were you out from the back injury? What's around your nipple area appears to be fat, not gyno. Unfortunately you can't spot reduce fat, but you can build and tone the area better. Do you train with dumbbells when doing chest? If so, is the side you had surgery on weaker? If not, try training with dumbbells to see if the area is weaker. If it is weaker, try doing some isolating movements to strengthen the weakened area. Also, you could be compensating when using barbells or machines. Keep up the hard work and you'll do fine.