Mothers of "birth mothers" - how did you find peace in your daughter giving your grandchild up for adoption?

I am 20 years old, single, and 21 weeks into my first pregnancy. I believe I have found hope in knowing that my baby will allow not just myself or the deserving couple I choose, but many more people an indescribable love and happiness. My family says they support what ever decision I make - whether to keep her or "give her up" for an open adoption, saying that no decision will be the wrong one - but I still see the underlying feeling of their being cheated of a great granddaughter, granddaughter, a niece, or a cousin. In my youth, as most can attest to, I have made my fair share of mistakes, disappointments, and hardships on primarily my parents. Is my only resolve to give them time? Am I supposed to be seeking forgiveness? I would really like another mothers take on what their thoughts and feelings were towards the "situation" and towards their daughter.