Does istibra' include anal sex before the marriage contract? And is it necessary to renew the contract in this case, taking into consideration the difficulty of that in society?

The act of anal intercourse before marriage that you committed is an abominable act and an act of fornication (zina) that necessitates the prescribed punishment (hadd). However, the marriage contract was concluded after repentance and remorse, and it is a valid contract. The Shafi'is and Hanbalis hold that anal intercourse is like vaginal intercourse in necessitating an 'idda (waiting period), whereas Sheikh Ibn 'Uthaymeen preferred the view that a fornicatress is not obligated to observe an 'idda; rather, she performs istibra' (clearing of the womb) with one menstrual cycle. You are not required to renew the contract.