The drywall won't hold, even if the fastner does. But you should be able to find another rafter - measure over 16" from the one you hit. If you don't find it there, measure over 24".
If you don't find it there, you may want to cut a hole big enough to stick a miror and a light behind the drywall and visually find the rafter. Or you can start 15" from the first bolt and cut across with a drywall saw until you hit wood. Then, you just have to patch a thin slice in the drywall, instead of a hole.