My advice is if you were told there was a mass, that you be sure it isn't cancer and won't grow anymore and cause you anymore trouble. With that out of the way, if they must do surgery, they should only have to take your right ovary to remove the mass, and you will still have one left, which means you can still have kids, if that's why you want to keep them.
You should still go in and make sure your sex organ health is okay, because putting off a problem now, may result in trying to solve a bigger and more expensive one in the future, followed by infertility. Try (if you can) on getting a second opinion if you do not trust what the doctors you are going to have told you.
I hope this helps you to decide what you would like to do. I wish you luck in all of your endevours.