As you sprayed it a week ago, it's probably dead and waiting to fall over.
The poision is in the root system by now, but you could try pruning it to
ground level which I have done with one of mine that was hit with a small
amount of roundup and not noticed until it started to go. It has sent up
weak shots over the last two years, but none of them has stayed around for
more than a few weeks. The stump is still there and I'll continue to leave
it in the hope something will grow, maybe I'll develop a roundup resistant
strain?

The different froms of roundup (or equiv...) normally have to be applied at
least two to six hours before rain and the best thing you can do is either
prune quickly and /or wash off quickly.

If you can mix up the contents of your spray containers and kill your wanted
plants, how well are they out of the reach of children? I hope you don't
keep poisions in old soft drink bottles!

Hope this helps,
Peter