Likely of being diagnosed with benign cyst, but turns out to be malignant

I'm 55. After over a year without a menstrual cycle and considered in menopause, I was uncomfortable on a 6 day bicycle ride and I had spotting after I returned home and urinary problems for the first time on a long distance ride.  My doctor found polyps and scraped them and had me get a vaginal ultrasound.  The ultrasound revealed a cyst of approx 4 1/2 cm, then an MRI and another ultrasound approx 2 months later the ultrasound show it's 7 cm.  My OBGYN presented the ultrasound and the follow-up MRI to an oncologist and she said the cyst doesn't appear to have malignant characteristics.  I understand my CA 125 was normal, but with all my reading, I'm not sure the CA 125 makes a difference in the initial diagnosis due to false positives and negatives.

I'm scheduled to see my OBGYN doctor tomorrow (Sept 12th) for a pre-op appointment and I'm scheduled to have my ovaries and the cyst taken out via laparoscopy on the 25th.  I don't need my baby making parts anymore so I'm thinking I'd like her to do a full hysterectomy.  

Although not considered malignant so far, they'll do a biopsy.  I'm rather nervous because I'm high risk: no children, over 50 and overweight.  I know someone who was told she had cancer and then they found out she didn't after doing the surgery.  

I'm nervous because I know I'm high risk, over 50, overweight and I've never had children.  I wonder how often one is opened up and the cyst removed and find out that it was malignant? I've had an aunt with ovarian cancer and breast cancer. She died when I was about 10 years old.  Don't know much about my Mom's side because my Dad took me and my brother away from my Mom who had custody of us.  She has since passed of respiratory issues.  I didn't meet her until I was 21.

I'm trying hard to think positive, but prepare for the worst because I do experience many of the subtle and common symptoms of ovarian cancer, but I understand from my reading these symptoms are similar with benign cysts. I also understand these symptoms are common with other diagnoses or can stand on their own as a medical diagnosis, i.e., nausea, heart burn, etc.

Symptoms of Ovarian Cancer  http://www.ovarian.org/symptoms.php
Ovarian cancer is difficult to detect, especially, in the early stages. This is partly due to the fact that these two small, almond shaped organs are deep within the abdominal cavity, one on each side of the uterus. These are some of the potential signs and symptoms of ovarian cancer:

Bloating
Pelvic or abdominal pain (sharp pain occasionally wakens me along with pain in back)
Trouble eating or feeling full quickly (not really experiencing that symptom)
Feeling the need to urinate urgently or often (yes, but was told that due to menopause and my body wasn't flushing out bacteria, therefore, I have a bladder infection although urinalysis didn't show urinary tract infection, but moderate number of leukocytes).
Fatigue (yes, maybe from depression dealing with this)
Upset stomach or heartburn (medicine is helping, but I'm most nauseous after eating)
Back pain (occasional now that I'm taking heartburn meds, but I feel sharp pain occasionally, but mostly dull pain)
Constipation (some) or menstrual changes (spotting for over a week after over a year in menopause)

From this site:  http://www.womenshealth.gov/publications/our-publications/fact-sheet/ovarian-cysts.cfm#c
What are the symptoms of ovarian cysts?  Many ovarian cysts don't cause symptoms.
Others can cause:

    Pressure, swelling, or pain in the abdomen
    Pelvic pain
    Dull ache in the lower back and thighs
    Problems passing urine completely
    Pain during sex
    Weight gain
    Pain during your period
    Abnormal bleeding
    Nausea or vomiting
    Breast tenderness

If you have these symptoms, get help right away:

    Pain with fever and vomiting
    Sudden, severe abdominal pain
    Faintness, dizziness, or weakness
    Rapid breathing