leaves about the size of my hand

if you scroll down the PDF,
there are some comparison notes and photos.
the flowers are different and the underside of japonica is less "hairy".
your plant looks a lot like F. japonica (japanese knotweed) to me.
With your closer observation, you should be able to tell for sure.

Here is a link that might be useful: identify F. japonica vs F. sachalinensis

thank you for the linnk I will check it out