If joining a weekend full of strangers feels like a stretch, you're welcome to bring one single friend — provided they are the opposite gender to you and they register separately.
That said — 85% of guests arrive alone and wouldn't have it any other way. The shared experience of not knowing anyone is a big part of what makes the weekend work.
Knowing you're all in the same boat is oddly liberating. By Friday night, it won't matter that you arrived alone.