Is it cancer?

I am 45 years old and had a hysterectomy nine years ago because of endometriosis.  I have been experiences some upper abdomaonal discomfort and knew something was not right.  Iwent for my yearly pelvic (3 months late) and my doctor discovered a mass.  A CT Scan revealed a 9cm liguid cyst on my remaining ovary.  My CA 125 was 47.  I am very scared and having surgery later today!  My doctor feels it is 99.9% not cancer.  I even brought my scan to another surgeon for a secon opinion.  He does not feel it is cancer also.  I though a CT scan can not detect malignancy?  And shouldn't I be concerned about my CA 125?  Please help, I need some peace of mind, or know if I need to freak!
I hope you can get back to me soon - I have been trying to post this question for a while no.
Thank you
chu chu