Get a second opinion, by all means. You can google the fibroadenomas and learn more about it. When you go for a second opinion, ask the doctor to submit you to MRI. There are also times doctor will perform the biopsy just to make sure that growth is not malignant. Do everything possible to completely rule out possibility of malignant tumors.
Wishing you the best of luck, get goint on this immediately, don't waste time.