Hi,
I am in the same situation, my left boob is prepregnancy size while the right one is big BIG! I have heard different opinions so I am not sure. One is that your boob will return to its original size after you are done with nursing. The other one is not as optimistic, it basically says that it may return to its size but will never look the same, it may actually be less supple.
To be honest, I was also obsessing about the size and how lopsided I am but I got over it at some point. I used to add an extra pad in my left bra to make them look even but now I don't. I know I am lopsided but I also know it is more in my mind because when I asked my friends they didn't notice the difference until I asked them. I keep thinking that the boobs are for my children and they were made for that purpose so I feel better about it.