It's alright to feel whatever your feeling right now. Hormones are playing havoc with me as well. The water guidelines are kind of redundant, especially if you have a small bladder. I drink a large iced tea 20 minutes before my appointments, and I'm usually sporting a full bladder. It's normal to feel shy spreading your legs in front of a stranger, and it never really goes away but you do start getting used to it over time.
On a sort of amusing note, the one time I had a male ultrasound tech, he was terrible. He was using the dildo cam and wailing around in there like he was Zorro trying to carve a Z on my uterus. I have painful large dermoid cysts and he was smushing them big time, making me gasp and tense up. He turned to his assistant (also a dude) and said quietly "Boy, she's oversensitive *gggle*" and I said, "I'd like to bend you over this table and smush your insidey parts and see how sensitive you are, buddy." lol he turned purple, and I commented to the nurse who was holding my hand, "God he's like a mechanic who's never driven a car, huh?" XD