If it was just after 1 class, it may be that your body just needs to get used to it, and after a week of indoor cycling, you might not have have any pain or discomfort at all. Kinda like when you stand on your feet a long time and you're not used to it, your feet hurt like crazy that evening... you do that after a few days and you hardly notice it anymore.
I'm not disputing any of the technical advice given.... just saying that my experience has been that that type of soreness goes away once you get used to the saddles on the stationary bikes. I'd give it a week or two before spending money on shorts.
~ working mom to 3 little girls ~
Roadie... 2010 54cm Trek Madone 4.5, Bontrager inForm