Thank you for your patience.
The reason I was asking all of those questions is to have a better understanding of you and your fiance. To give you your answer I will go down the list and summarize the most important factors that you need to be aware of.
First of all, until the child is born, you, for the most part, have no rights to the child. It is the sole right of the mother
to choose to bring the child to term or to have a procedure. Similarly, it is generally up to her as to whether or not to seek out a possible adoption. You can petition the courts early yourself for a paternity
suit and request testing, but until you are not deemed to be the father, you cannot make any formal decisions here. Similarly, if your fiance decides to be difficult, she may choose to not place your name on the birth certificate, forcing you to file for a paternity hearing and order via the courts. (Not stating that will happen, but it may).
Second, the courts generally base their decisions on "fitness" of parents and on what they deem to be in the "best interest" of the child. That means that if you want custody, you must show yourself to be more fit, responsible, and able, and attack her fitness from the conditions I defined above. It is not likely that you will get custody, all factors being equal, without your ex being shown as someone who is dangerous or otherwise not someone who should be around children.