Being only 2 days since surgery, you have some time (2 months plus) before seeing the final result as your tissues will relax.
As you have said, the cup system can be variable but looking at your torso I think you will be a C/D size (pending bra brand) when you have healed and have better...
If you can detect a difference in the firmness of your breasts, especially if it's the left one that's firmer, then most likely you have some degree of capsule contracture. The classic findings in the case of capsule contracture are firmness of the contracted breast and upward displacement...
The best way to predict cup size changes and cc of the implant is to wear a bra and put that many cc of volume in the bra and look in the mirror.
Some use bags of rice and surgeons will often use an external sizing system. This way the volume needed to be added to what yuo have...