Particularly with younger women such as yourself. (You may not think of yourself as younger, but for this you are.)
The reason is that breasts change over time. Younger women have more natural variations that look like a potential lump. That's the big reason they don't recommend regular mammograms earlier unless you have a family history of breast cancer.
And, assuming that we're talking about a breast biopsy, your odds of survival are high. Your fear of "OMG, I could DIE!" is very real. That can happen. But we hear about breast cancer because most people survive it, and lots of them go around talking about it.
Still, good odds or no, I'm hoping with you that this scare resolves itself as quickly as possible.
Cheers,
Ben