I would say join 2/3 societies you're really interested in and make an effort to attend events as often as you can. If none of these work out, then maybe think about finding a different one to join. If you join 5+ societies, chances are you won't end up going regularly enough to make friends, and so you'll end up not going to anything.
Secondly, don't think of confidence as innate- something you're born with or you're not. Think of confidence more like a muscle- the more you exercise it the better you get. In other words, fake it until you make it. Speak to everyone, say hello. On freshers, everyone wants to make friends so talk to as many people you can. Go to everything people invite you to if you can. Make an effort!
I'm not saying this about you OP, or others on this thread, but some "introverts" can come across as quite arrogant. They expect people to chase their friendship, when they're shy and standoffish, and never make the first move. They expect people to keep inviting them out, even when they've said no, the last three or four times. They don't make even a reciprocal effort, and then wonder why they don't have close friends. If you're really socially awkward, at least let people know, because otherwise they will think your responses mean you don't like them.
Everyone is trying to make friends during freshers and the first term of uni- so don't worry about how you come across, just make an effort and you'll meet some great people. Your confidence might even improve a bit.