Need reassurance

Sarah • First baby Thomas Declan 💙
I am 12 weeks today and just got a letter saying my first scan is in 4 weeks when I will be 16 weeks to the day. 
I am petrified of waiting so long to see everything is ok. What if I have a blighted ovum or baby has never developed?
I have had lots of pregnancy symptoms and think I can feel the start of my uterus rising above my pubic bone but of course this is my first baby so I have no idea what I'm looking for. 
I am constantly worried and I feel like crying im so emotionally drained