How to relate to the masses and dominate a group conversation?

Tonight I was hanging out with 4 girls (7, 6, 5, 5) and 3 guys. I wasn't trying to get with them or anything. We all went to school together, so it was very casual and friendly.

We hung out in the hot tub, talked and what not. I wasn't trying to game anyone, rather I was simply practicing to become the dominant presence of the group.

I failed. I simply couldn't relate with these people when they discuss things like sports, gossip, celebrities, etc... While I wasn't the dominant presence, I wasn't secluded or very quiet either. I just failed to become the source of energy and vigor that everyone synced with and observed by default. I failed to become the alpha.

I'm naturally quiet, but I'm trying to get over it and become an extrovert. Any tips to achieve this next time, especially when I can't relate to the conversation?