I'm sorry to hear about your difficulty with this whole situation, this kind of stuff can be very scary. Hopefully I can ease some of your worry. I'm not sure if someone explained them to you, or if people here don't know, but I thought I'd share just a little info about them.
A dermoid "tumor" is the most common solid tumor in adolescent and reproductive age women, compromising 20% of all ovarian tumors! They are really kind of cool - they are called germ cell tumors, meaning they arise from germ cells (your eggs). So when a tumor (or cyst, as some call them) forms, it contains "human things", like hair, teeth, bone cartilage, and fat - lots of fat. Your doctor was correct, in that you have a high risk of ovarian torsion (twisting of the ovary, which cuts off its blood supply). The reason the risk is so high is because of how much fat is in these tumors - it causes them to "float" up in the pelvic cavity, and that just makes it easier for them to twist. So you will need to have it removed
However, you can rest easy on the fact that only 1-4% will become cancer, and even if that were to happen, they are HIGHLY responsive to chemotherapy (ie: they can be treated easily and successfully). So really, you don't have to worry about "ovarian cancer" - this is not the kind of tumor that is associated with the "deadly ovarian cancer".
Having a tumor is definitely scary, and I completely understand your fear and concern. The risk of torsion is real, and something you want to be aware of and have taken care of, but otherwise, you don't have to really "worry" about it.
I hope this helped. Looks like you had an appointment today, so I hope that goes well and everything gets taken care of!
Best of luck, and many blessings!