OP, want to give you a hug! We TTC for 3 years, failed IVF, etc, the whole journey. When I saw the two lines I was delirious with joy and worry, and ... well, fast forward 10 months, and the joy and worry have never stopped!
As far as when it feels more real: for us, with every step closer, I guess!
After my home preg test I thought it was too good to be true. My husband even said I was imagining the lines of the 10 preg tests I laid out for him - LOL!
The first beta at the RE: yes, it's real, but will it 'stick'?
The heartbeat on the 6 wk sono was a big one for us! ... at the same time you 'graduate' to your OB.
It felt more and more real then with every sono, every 'congratulations', with every ritual such as walking through a baby store to register, ...and you mentally check off your milestones: made it through first trimester, found out gender, first movement, third trimester, viability (that was also a big one for me)...
But nothing, nothing beats the moment when that little baby finally comes out!
So Congratulations!!! That worry is normal, as I said, never stops, and at the same time a sign that you are becoming a mom!