If you are planning on growing veg. in the area you have dug do not use weed killer. Dig over again and remove the weeds.

Annual weeds like groundsel will rot and perish when dug in. Perennial weeds like docks and dandelions will come through no matter what time you dig them in, so these long rooted types need to be removed from the soil completely and taken to a compost bin (better still, stick them in a black plastic bag to rot for about a month, and then add to the compost.)
I agree with Moon grower that weed killer is best avoided. The only 'safe' one (and that is now debateable) is glyphosate ('Roundup) but you have to leave that to work on the growing weeds for several weeks.
Unless you are gardening on a huge scale, it's really not that difficult to clear the ground with careful digging and then use a sharp hoe to keep the weeds down as they appear.
In any case, in a flower garden using weedkiller risks harming the plants, while in a vegetable garden you get residues taken up into something you are going to eat.

its not a problem to dig it again,thanks