You'll have the strength when you need it. You'll be a Mom - and having that inner strength is just one of the things Moms do.
When my son was born he was a week late & weighed 6lb 11oz. We had not a clue that he would have DS .... and I'm glad I didn't know. I would have been scared and worried about all the what if's and I would not have been able to enjoy the pregnancy. Yes, it came as quite a shock to us - yet somewhere deep inside ... I did already know. The only "sign" that something might be wrong prior to his delivery was that he never moved much - and when he did, it was very faint, just a flutter was all. That will soon be 8 years ago. Today, he don't sit still long at all.
I can understand your anxiety .... just enjoy the last few days of your pregnancy, and comfort yourself in knowing that only for this short time will your baby's world revolve around nothing but you.