Just flexing your hip while seated or sitting normally can change you erect length.
I gain like 1.5 or 2cm just by flexing my hip out while seated, maybe you did that and it made a modest gain seem crazy big!
Truth is the tissue, or even the ligament can’t expand that much in a week without being destroyed.
Anyways, I hope you hit that 8” mark, however try to consider girth in the equation more, if not more than length, that is what she would notice much more!
The main problem with girth (what I really love it, don’t get me bad) it’s that when you have to much girth or the girth it’s looking like with the lenght, your penis looks like he’s smaller.