Dry hopping in a carboy, as the OP did, and using bags is a bad idea. Pulling a swollen bag through the skinny opening is a PITA. Just toss them in. Use the proper size carboy, so you can fill it up to the neck so that the hops have no place to float. Cold crash after a few days and they will drop.
In this picture there's only about 2 1/2 ounces of hops, but you can see how well they've settled to the bottom.