Birads confusion with biopsy results

My lumpectomy is scheduled for Wed. I just got the reports from the ultrasound they did before the core needle guided biopsy. They were rating the mass at the ultrasound before the biopsy as a birads 5 highly supicious of malignancy. But the biopsy results came back as b9 fibrosis tissue. The ultrasound also said it was spiculated. I also read that the biopsy results are discordant with the imaging.They are doing a exisional biopsy. Should I worry it's cancer? What are the odds?

Thanks