Yea...that's how you figure out what's right for you. Ummm...there are other sites that I know for a fact run smaller than underworks. You're either really young or have a tiny frame.
You can try here:
http://www.lesloveboat.com/shop/index.php?language=enThey are made for smaller bodies...the smallest size might work for you...I know they use velcro on a lot of 'em so the tightness can be adjusted.