Going by your query it appears that you had a consensual sexual relationship with the girl. I emphasise the word consensual. Consensual means having her consent. At the same time it was also made very clear by you, since beginning to her that you were not committing to marry her. If, with this full understanding she entered the consensual sexual relationship with you, (and assuming that both of you are adults having crossed 18 years of age, at the time of indulging in the first sexual intercourse), there does not appear to be anything illegal with what you did.
The problem stated by you appears to be that she's now after you and your family, forcing you for marrying her, which you do not want.
But the potential problem that I see is that (and please do not misunderstand me to mean that I'm instilling some kind of fear in you, and that's why I have used the word "potential") in the event of you refusing to marry her, or your family not permitting you to marry her, if she gets provoked, she might lodge a false claim of rape against you, in future, and that might land you in trouble. This is only a possibility, and may not even turn out to be true. So just don't be panicky.
For such an eventuality (I pray to Lord, that they should not happen with you), you will have to prepare yourself beforehand by collecting, and keeping ready with you the bits and pieces of evidence which would prove that the physical relationship that she kept with you was with her full consent. So, start collecting such bits and pieces of evidences about the consensual nature of your sexual relationship with her, from whatever sources possible.
In addition, you may also get her oral admissions with regard to consensual nature of your physical relationship recorded either on phone, or during face-to-face conversation. And carefully preserve such recordings for future use.
As regards she harassing you and your family members, I would suggest that the best way to handle the situation would be to handle it tactfully, and in any case avoid provoking her or any of her family member so that either she or they may not land you in further criminal legal trouble. You will have to figure out ways to do this, for yourself.
In the event of any possibility of any such criminal case being filed by her against you or your family members, in future, be prepared to secure anticipatory bail from the concerned criminal Court in your area.
But for the time being, handle the situation very tactfully and make efforts to convince her and her family members that it may not be in her best interests to marry you.
All the best!