Mike, in tandem to what Freak is saying...
Are you practicing holding your poses for a few seconds and truly flexing them for a count of 5?
I didn't my first time around and by the night show I was soo sore, felt like I just did 1000 sets for every body part.
As for nerves...as they say, pic a geek in the crowd, perhaps me if I can go and picture this person in a clown outfit or something ridiculous...it will keep a smile on your face amd lessen the nerves
As for the banana hammock, this is normal, just don't hike it up your ass and make sure you buy some of that posing trunk glue (Freak help me out here as I can't remember the name), will keep you from fidgeting...