All the women on both my Mom and Dad's side of the family has C or larger cup breasts. I am now 18 and I am still a 32 A, almost a B. The areola part of my breast is rather large, though. Does that mean I am still going to grow more? By the way, I got my period when I was 15 years old, so am I still going to grow more? I really want to know. I'm sick of waiting!
And why aren't you happy with who you are instead of imagining that if some dimension of your body was different then you could be happy?
The likelihood that you will grow more is very slim, but only a doctor could tell you for certain. If you have reached stage 5 in development, then you will not be growing any more. You can check by taking the quiz at Tanner Stage Calculator for Girls. Your breast size is based on the genes you inherit. Just as two dark-headed people can have a red-headed child, you can inherit a combination of genes from your parents that leaves you slimmer than your mother or grandmother.
When you start having children, your breast size will increase a bit, but that is about the only change that will remain. Learn to be thankful for what the Lord has given you instead of demanding more.