Scared and nervous here - "suspicious" finding on my breast u/s

First time here and have been searching all over to find some support.  I may be freaking out over nothing, but here goes:
OB/GYN found a lump in my left breast (I can't feel it) so we did a mammo.  Mammo was negative, but I have very dense breasts.  Did U/S and here is the report:
Findings:  An ill-defined heterogeneously hypoechoic mass is present in the 12:30 position.  6 cm from the nippleThis lesion demonstrates angulated margins and possible posterior shadowing.  The dimensions are 7 x 7 x 4 mm.

Impression: Irregular mass in the upper left breast which is suspicious sonographically.

Next is u/s guided biopsy, which I have to schedule on Monday.

I'm scared it's malignant.  What are the chances?  I can't feel this (it's small).  What if I didn't go to the doctor?  I would of never knew it was there.

My doctor was telling me not to freak out and she sorta brushed this off as nothing but recommended a good breast center in Monterey, CA.  

Anyhow advice or comments would be greatly appreciated!!  THANK YOU!

[Cleveland Clinic]

Dear librafamily:  The ultrasound detected an abnormality that cannot be further characterized and therefore, a biopsy is recommended.  There is no way, based on this information, to speculate on whether this is benign or malignant.  Hopefully, you will get the appointment soon.

[ski1023]

I know it is scary to wait.  I was told Thursday I need a biopsy but could not schedule yet due to looooooooooong weekend.  Hope we both get some answers Monday. Good luck and I am also trying not to freak out.  I am very practical and worrying is ineffective.  Plus if I am going to have a negative outcome I'll have plenty of time to worry later.