Can I extend x2 type visa without leaving China?

Mary, it's up to local entry and exit management bureau. You can try to extend X2 by providing the proof that you need to study another semester, such as a letter from your school. It should state that you are studying and you need to extend your X2 for another semester. Besides, admission letter is required. I think you might ask help from your school. They should be able to help you.

If your extension request is denied, then you need get back to your country to apply a new X2.