Story & Questions... concerning?

hi, i am very new here and this is my story/questions.

I am 29y/o, over all healthy. I noticed a “cafe au lait” like rash in my cleavage area that has been spreading over a few months time. I decided to do a self exam, since i haven’t in a few years. I found a rather large lump in my right breast. Called a highly recommended breast surgeon in the area. They performed an ultrasound as it was visible from the outside.

Here’s where my confusion lies:

The radiologist said it looked much like a Fibroadenoma. He said he wasn’t concerned, and in the same sentence recommended a core biopsy to be sure. I went and met with a nurse. She explained everything to me. She said there are areas that are not concerning at all, and others that signify malignancy. She said he was being confident with recommending it was a Fibroadenoma, most likely to make me feel comfortable. They put my BIRADS score at a 4. As i am self pay, i asked multiple times if it’s absolutely necessary and that if they’re confident it’s begnin, I’d come back for a follow up. She stated that wasn’t an option and they want to do the biopsy ASAP.

Does it sound like they’re just trying to not worry me? If he was confident it was a Fibroadenoma, why would he put my BIRADS at 4?

I know I’m in my brain too much and I shouldn’t worry... but easier said than done.

TIA