Yes, the "bike pants" fit is what you want -- not loose, but not tight so that you can't move. If it is too lose, you'll be carrying around water and pumping it in and out those "seals" every time you bend. I know from experience that chills you pretty quickly. Then again, a 1/2 mm suit isn't much insulation anyways, so I'm guessing you're diving in relatively warm water (compared to what you'd be comfortable in with just a swim suit).
Herderson is the only off-the-rack suit that comes close to fitting me, being 5'9" but with a 29" waist. With 2-3% body fat, I need all the help I can get and taking the time to find a suit that fits right makes a big difference. Its still not-quite form-fitting through the waist, but certainly no wrinkles or sags, just 1 cm or less of gap along the spine.
I'd see if the next-smaller size fits you. Shoot -- you'll look better in it at the bar after the dive too!