Im so terrified. :( Babys not growing

At my 21w ultrasound to see if my baby has Spina bifida (which she doesn't), she is measuring 2 weeks behind. :(((( my placenta isn't giving her enough nutrients and my fluid is low. She is only measuring 19w4d :( the doctor is having me come back in 2 weeks to see if she progresses (grows), if not, they have to put me on medication for nutrients for her, if that doesn't work, I have to deliver early. :(((((((((((((( I'm trying to stay strong but it's hard