How long before you get the results of the biopsy? In your shoes, I wouldn't decide on a hysterectomy before hearing what the results are. A thick endometrium does not automatically mean cancer.
Has there been uterine cancer in your family? Do you have diabetes? What's your weight? If the answers are no, no, and not obese, even with a thick endometrium, you have a reduced chance of getting uterine cancer. Also, what time of the month was the visit to your ob/gyn for the ultrasound? Just before your period or just after? If I were your doc, I'd be interested in seeing the thickness of the endometrium right after your period.