I read about a study linking menstrual cup use to endometriosis. i am very worried. can i get endometriosis from using a menstrual cup?

No: There was one case report of a patient using the menstrual cup who got endometriosis, but it is not clear what the relationship was. A larger study in Canada showed no difference between the menstrual cup and tampon use for causing problems.

"Cup runneth over": Endometriosis is thought to occur by menstrual flow "backing up" into and through the Fallopian tubes , flowing into the pelvis and "seeding" the pelvic structures and lining of the body(peritoneum). If the menstrual cup is placed properly and tightly, and not emptied regularly, then you will test our theory of menstrual "backflow" and consequently the potential for Endometriosis.

Theoretical: This is based on the retrograde menstruation theory and other experimental models where menstrual blood is projected back into the abdominal cavity to "produce" endometriosis. To my knowledge there has never been any evidence that menstrual cups produce endometriosis. This is merely a stretch from these studies. It is however also not proven that the cup does not produce endometriosis either.