Blackmailing me to sign an affidavit

My husband have applied for divorce, and as per settlement deed he has custody for 20 days in a year. The second motion for mutual divorce has not been signed. We mutually decided that he will take my daughter for 4 days and return her back but he didn't return her back. I went to police, they said you have applied to court so only court will help you.i checked with lawyers if they can help me get back my daughter they said we can apply for high court but after decision it might take from 1 month to 4 months. He blackmailed me to write an affidavit and notarized it that I will sign the property papers to him then only he will return my daughter. So I was forced to sign the affidavit and have it signed my notary and gave it to my husband then only he gave my daughter back after 7 days. How can I inform the authority that this affidavit was signed due to blackmail, I have all the proofs pertaining to blackmailing. There are other clauses in affidavit which is a trap for me in future. Pls help and guide.