Fit of traditional cycling shorts

I am ready to take the plunge and purchase "real" cycling clothes. I rode my first metric century on Saturday and my butt was so sore that it was hard to enjoy anything after the 20 mile mark. My question is to fit. How are those high compression padded shorts supposed to fit? Should they be super tight in the rear and legs, or a little loose? Do they shrink? How much should I have to wiggle and work to get into them? I need some pointers. Also, I tried on a Terry skort today and loved it, but again have questions about the fit of the shorts. Unfortunately, the guys at my LBS are clueless when it comes to women specific clothing. Help!

the shorts should be tight, but not so tight you can barely squeeze into them and certainly they shouldn't cut off your circulation. you don't want them loose, because when you get up off your seat they spare material can hook onto your seat (has happened mountain biking, not so fun). When i try mine on, i see if there are any loose parts bunching, and i give the shorts a little tug in spots, and see that they "bounce back" so to speak. some shorts are less stretchy than others. i try to avoid those, since a friend bought a pair and now they are HUGE on him. i mean like boxer shorts. I have never had any shorts shrink, what you buy is what you get.

good luck
Han