couldnt read and not respond. so sorry to hear of your situation. firstly, you are most definatley not a terrible person. it is however a terrible situation.
i very much related to your post as i too went through with a medical termination for trisomy 18. All the reasoning in the world still doesnt negate the tearing at your heart but in time it does help.
brusselsprout has sound advice in suggesting seeking counselling. sids n kids also help women and families with this situation.
and agree that you do have options. i delivered in hospital and got to spend some time with my baby. but you have to do what you feel most comfortable doing.