Well first of all, well done to you for going

Though starting out with a spin class was perhaps a *little* bit too much... I've seen those in action and I wouldn't dare try one!
I joined the gym about 6 weeks ago now... had never been to a gym before in my life so I'm UNBELIEVABLY unfit. But all of a sudden I was going 4 times a week, doing 2
Body Pump classes, plus an
Ab Attack class and then doing at least two 1/2 hour sessions of cardio as well as a personal training session which includes lots of abs, biceps, triceps & leg workouts etc.
Don't give up on it, but if you're in that much pain then do rest for a few days. When you go back perhaps you should try something slightly less intensive such as going on an elliptical trainer; start on a low level and do just 15 mins or so the first couple of times and gradually build it up to 25-30 mins+ and increase the intensity levels. You will ache a bit the first few times but your body gets used to it quite quickly.
I hadn't been to the gym since Christmas Eve as I was away from home for a few days. Went to a pump class earlier on and oh my god, I am aching now. I've just made a cup of tea... my arm hurts just from lifting the kettle

Perhaps I should've lowered my weights today!
Some things I've figured out....
- build it up gradually (e.g. on the elliptical trainer thingy) but do push yourself a bit more each time so don't just stay on the lower levels
- do some stretching afterwards - especially your quads. if you don't know how to do this then ask one of the gym instructors to show you.
- a warm bath can help if you've had a hard workout!
good luck with it
