When my mom has ovarian cancer, how big is the chance that I've got it too?

Your odds are getting this are increased and since this is such a "sneaky" cancer you have to be more alert and watch for the symptoms without being obsessed with every sign. Watch for a lot of bloating in your belly, increase bleeding during your period, tummy pain,weight loss, and/or change in bowel habits.
Don't worry yourself to death either tho.
Good luck.

they are pretty rare i am going to provide a website but here is a section of it i found explained it best

Some situations make it more likely that a certain cancer is caused by an inherited gene change rather than being sporadic. A cancer is more likely to be inherited if:

there are two or more close blood relatives on the same side of the family affected by the same type of cancer....a close relative had more than one primary tumour. This means that a person has cancer twice, but the second cancer is not due to the first cancer spreading to another part of the body: it is in fact a new cancer (for example, breast and then womb cancer)...members of a family get cancer at a younger than normal age (under 60 years)certain cancers happen together in a family. There are two main patterns where cancers occur together.

all depends, just make sure you get regular cheak ups so it can get caught early if, any chance you could have it.
but you needn't worry though, some people don't get their families history & genes.

If cancer runs in your family, other than your mother, you have a higher chance of getting cancer. However, it is rare for a mother and daughter to both have ovarian cancer. It is more likely for you to get cervical or uteran cancer if she has ovarian.

Make sure you keep track of your periods, if they get heavier than usual or if you have severe cramping in between periods go see your GYN as soon as you can.

Hope this helps!

It's a bit increased as well as your chances for breast cancer because your mother is a first degree relative.