Kayla, it sounds like your circumstances have made a very difficult situation much easier. Your adoptive parents sound like lovely, caring people; the social tie you already have will help bind your relationship; and open adoption is truly the best way to go for the birth parents, adoptive parents, and the child.
I would suggest that you speak to a lawyer to review whatever documents you sign and discuss what legal status your open adoption agreement and visitation rights will have. You will also have to sort out what role, if any, your baby's birth father can and should play. Again, your relationship with him may be sour now, but it will be better for everyone involved if he can continue to play a constructive role in your child's life.
My deeper concern, though, is that your circumstances are far from typical of birth parents who place their children for adoption, whether domestically or internationally. There are two kinds of fantasies many people, especially adoptive parents, have about birth parents. The most common is that they have rescued their children from a horrible fate, especially from their horrible, accidental parents (almost always people of color).
The other is the "spa adoption": a beautiful, intelligent, birth mother (almost always white, almost always a college or college-bound student), who chooses to forego raising her child for a combination of altruistic and self-empowering motives, and who then is pampered, cared for, made a part of the family. (The same fantasies are usually advanced for egg donors, nannies, or any other kind of proxy parent.)
There are birth parents who conform to the former stereotype as there are birth parents who conform to the latter. But in the majority of cases, the reality isn't just in between, but radically different, infinitely more complex -- tragic and romantic, comic and quotidian.
I think that your story will grow more complex as you and your family grow, and as you continue to process your feelings. There will be infinite misunderstandings -- with friends, with family, with future friends and future family, and with your child, his/her adoptive parents, and even wth yourself. But stay close to your child -- he/she is the only one who matters.