YMCA sd

I was thinking of getting a YMCA membership because it’s like a regular gym plus they offer a bunch of yoga, Pilates & barre classes but as I was looking through the schedule today it all seemed super booked out so I was wondering if any of you with a YMCA membership could give me some insight like is it hard to get a spot in those types of classes do you need to book super in advance like what’s the vibe??