The best thing you can do for your girlfriend and your child is comply with your service obligations. Call your recruiter, and see if you can be slotted for a later reporting date for Basic Training (it sounds like you are under a delayed enlistment program).
If you intend to get married, now is the time, because all armed forces have an excellent health care plan for servicemembers and their spouses (have you looked at the cost of having a baby?).
Once you are on active duty, remember, there is absolutely nothing that you can say or present to a Sergeant that they have not heard before and have helped handle.
