Why do they send us so early? A due date doesn't need to be so exact!!!!! I refused to go for a dating scan this time as it caused me so much stress with DS1.

Apparently the cycle that I fell pregnanct with DS1 was over 5 weeks long... the first time ever. I went for my dating scan thinking I was around 7 weeks for them to tell me that they could find a heartbeat. What seemed worse at the time was that the sac was measuring exactly to my original dates.
After lots of googling ( which you should never do) I was convinced I had a blighted ovum and spent the next fortnight completely miserable. When I went back though, they found the heartbeat and everything was perfectly fine.

I can't promise you that everything is fine, but it was for me. This definitely happens, and you said yourself that you went because you were not sure of your dates. I know how it feels but no amount of worrying can change anything. Go back for your next scan and please try not to beat yourself up too much before then.