I don't know if this helps or not, but this is my u/s at 5w, transvag. Just a little black spot. At 6w, we could BARELY see his lil heart beating on the screen, but at 7w, we could hear it and it was beating nice n strong.
I used the ClearBlue Digital HPT's, so I have no experience or advice to offer with the lightness/darkness of the lines.
Hang in there.

everything is ok with your bean!
