Mistake on Study Visa

Greetings

In March 17th, 2017; I aply for my Chinese student X2 type , to Take a course on Chinese Medicine starting on August 4th, 2017. Once the Visa was issued i notice it says on 'Enter Before' June 17th, 2017; with 90 days of duration of stay.
I think this Is a mistake, or there Is something i might not be understanding. Would this affect me If my day of exit China Is on November 8th, 2017? What can i do?
Thanks for your attention.

Best regards
Yonatan Indart