In answer to your question, since it was your first time it was probably nothing to worry about. For me though, I ride mostly with guys so my experiences may be different to you. What happens though is some of the more experienced riders in the pack will be observing everything - they know when you join the group, if you are struggling, if you drop off, if you take a turn and if you just sit at the back and draft because you're being lazy. This said, if they can see that you are struggling it is acceptable to "sit on" because they do want you to be able to get home. However, if you are strong enough to do turns and are being lazy, this is unacceptable and the rider in question will generally find themselves pretty unpopular. My policy is that for the first 3-4 times on a particular ride it is ok to sit on, this will give you time to build your fitness up, but after that you should attempt turns even if its for only 1 or 2km. Personally I find as a chick that if you get to the point where you do turns at a good pace with the guys, then you start to earn their respect as a cyclist