Congratulations! One miscarriage doesn't always mean another BUT having been there I KNOW the anxiety you feel in the first trimester and even beyond. Miscarriages kind of steal away this bliss that anything could even go wrong, at least for me.
I say that you sound like you want to wait until the sonogram. So wait until the second sonogram and you feel comfortable.
Also dates can be off by 1-2 weeks. Do you have longer cycles? Did you ovulate later? If so that could be why your dates are a few days off. Implantation could have also happened a little late. There's nothing wrong with that or your body. Also ALL of these dates are estimates.
Good luck and congrats again!