i agree with everyone that people fret at scans- my pregnancy was unplanned and i had been on medication for al ong time beforehand (and the early months when i didnt know) so woried the whole time i was pregnant, i now have a beautiful 3 week old baby girl who is completly healthy.
its easier said then done to not worry but in reality its only a percentage of babies that are born with defects- the vast majority are fine
however if it does turn out theres something wrong then you will deal with it. You seem so adament you couldnt have it terminated that you would have the baby and even if it only had a short life expectency you can use that time to fully enjoy your baby. Take every moment for what it is- a blessing! and be aware that even people with short ife expectencies is only an estimate, they'll never know for certain.