Consensual sex with 17 year girl on promise of marriage is offenc

Am in love with my girl friend.her date of birth is [deleted] in ssc memo.but her actual date of birth is [deleted]. i had sex with her on [deleted].and she has given consent for sex on mutual promise od per ssc memo she has 17 years per date of birth certificate she has 18 years now..i have phone call recordings of my girl friend words spoke to me that she wants to marry me.i want to marry her in future.she is in house arrest now.their parents know my love story.their parents gave warning to me.after may 5th 2017 i want to go to police station nd talk to my girl friend about marriage on that day.if she rejected my love then how to marry her.i have all the proofs (phone call recordings, messages love letters) that she loved me nd consensual sex with me. so if their parents booked rape case on me shall i booked under rape case.bcoz as per ssc she has 17 years on sex participation date.if their parents booked rape case on me how to proove that she given consent for sex,and which certificate is valuable d.o.b or ssc to escape from this case and how to marry her if she rejected me.can i file cheating case on her to cheat in promise of marriage.