Misdiagnosed abnormal pelvic mass

[davismavis]

Recently I went to my OB for help with an issue of bleeding between periods and heavy periods. She ordered an ultrasound. When we met to review her findings she said she was concerned about the heavy bleeding, but more importantly she found a "large, abnormally shaped mass spanning both ovaries". She told me that the nature of the mass was so complex that she does not think she should attempt to remove it herself (she's a surgeon), and thus referred me to a Women's Cancer Center for mapping and removal of the mass with a possible hysterectomy the following week. My CA-125 came back normal sometime between appointments. After an excruciating emotional week, I had another US by the referred Women's oncologist who concluded that the "large mass" looked more like fluid.  She said it seems like maybe you had a cyst that ruptured and it filled this area with fluid and that my body should absorb the fluid over a few weeks.  And YES THAT IS AMAZING, GREAT, WONDERFUL NEWS!!
But what should I do from here? I trust the oncologist... but I also trusted my normal Dr. until now... Isn't this a big misdiagnoses? How often is fluid mistaken for a solid mass on an US?

I am not sure how to move forward. Would a 3rd opinion help in this matter? Do I call and make another appointment with my normal OBGYN after this rabbit trail and try to trust their new discoveries, or do I get copies of my medical records and look for a new OBGYN? I am just worried that ONE of the two US are wrong... I can't get over it!