In a large group ride (20+ riders) it is common for the group to take up an entire lane. This is outside of your individual control so don't worry about it. If you are riding on a road that has 2 lanes, however, it is your responsibility to NOT USE THE SECOND LANE! Motorists hate us enough for taking the first lane, but blocking the second one is just asking to get run over as they speed by. The cyclists don't like it either, it makes us look bad, but more importantly, it shows your ineptitude at being able to move up through a pack.
The same is true for a yellow line. Don't cross it to move up in a pack. In a race it will get you relegated or kicked out, in a group ride it will get you yelled at, or killed. If you can't move up through the lane that has already been taken up by the group, you need to move slowly through the pack, not into oncoming traffic. Again, this makes us look bad, and it makes you look bad.