Wait 10 to 14 days(some will recommend3 weeks), then take a reading. If it is near your FG, take another reading a few days later. If they match you're ready to go.
Putting your sample back in risks infection, so don't do that. But don't dump it either! What a waste of delicious beer. You should always taste the sample so you can learn how the beer changes, and also see if it is propely conditioned.