Regarding expiry of china visa

Dear Sir/ Madam

My self Satish from INDIA , right now I am in china with extended category F,
I have some of query regarding my visa as below.

My F issue date in India is 18th September with duration of each stay 30 day after entry. and enter before 18th December 2012
Travelled to china 23rd September
Extension is issued in china on 22nd October
Extension got up to 31st December 2012. (mentioned Valid until 31st Dec 2012)
Total day stay in china will be – 98 days

From some sources, I heard that, Only 90 days is the maximum period for Indians.

So request you to please confirm, can I travel on 31st Dec.
or I need to travel before 23rd December (i.e. only for 90 days)

Request you to please provide the feedback